Animal rights groups are calling for the immediate closure of a laboratory in Germany after the publication of a harrowing undercover video.
The eight-minute footage, released by SOKO Tierschutz and Cruelty Free International, purports to show monkeys screaming as they're strapped into upright positions in metal neck braces and their arms restrained on rests.
Dogs are also seen standing in cages that appear to be covered in pools of blood, while others are strung up after their death.
SOKO Tierschutz and Cruelty Free International say the footage was filmed at the Laboratory for Pharmacology and Toxicology (LPT) in Mienenbüttel, south-west of Hamburg, by an undercover agent working as an animal keeper assistant from December to March.
Local authorities have launched an investigation and said no more approvals will be given for animal testing until it's concluded.
The laboratory said it is cooperating fully with the probe.
"You can only do this [job] with thick skin," the agent later told Euronews. "And with talking to the most active people after work, it's damn hard to bear."
When asked about the most difficult part of the job, the agent said: "Standing in front of the kennels where the animals lie in their own blood and there was nothing I could do."
In a further statement, SOKO Tierschutz claimed the dogs being tested were left "bleeding horribly" after "being forced tubes of capsules" down their throats, with many later reportedly dying.
It added: "It is shocking to see how these dogs consume after affection and care, and then have to die so pitifully in their blood."
According to the animal welfare group, the monkeys had it worst with "bloody injuries" during experiments, and the reported case of one employee who "deliberately slammed a monkey against the edge of a door".
"Resistance to such attacks is meaningless," one employee is said to have told the undercover agent.
The agent was also asked if the lab's employees were emotionally blunted by their work, who said: "Most people don't seem to care about anything.
"They have become completely dull over the years. A few people want to improve or report things, but are not able to assert themselves."
In one experiment for a veterinary drug company, the group said some of the lab's cats were injected "`13 times in a single day."
"Again, the staff lacked skills, which resulted in consequences for the animals."
"Most studies end with the death of animals," the statement continued, before referring to a section of the video that shows several dog corpses being strung up on hooks, while another is butchered on a bench.
It also shows an image of a cat's corpse at the bottom of a bin bag.
SOKO Tierschutz and Cruelty Free International are now calling for the lab to be closed and an "immediate end to the outdated, dangerous and cruel animal toxicity tests".
"Our research reveals appalling animal suffering, inadequate care for animals, bad practices, and breaches of European and German law," Cruelty Free International's Michelle Thew said.
"We call for a comprehensive review of this case and all such animal testing in Europe."
The laboratory said in a statement to Euronews: "We carry out studies for customers in the course of drug approval. These are pre-clinical tests of a substance for toxicity before it goes into clinical testing, for example: tested on humans.
"These studies are required by law and are approved and supported by the authorities.
"Animal husbandry is also required by law and is monitored by the authorities, including unannounced inspections.
"We are cooperating fully with the authorities in the current investigation.
"We ask for your understanding that we cannot comment further on ongoing investigations."
Rolf Hömke, from the German Association of Research-Based Pharmaceutical Companies, said that currently "new drugs cannot be developed without animal testing".
He added: "To refrain from animal experiments would, therefore, be irresponsible."
"If an alternative method is appropriate and legally accepted, it will be used immediately.
"However, a number of animal-free or animal-saving test methods are still waiting to be accepted internationally by the authorities as a replacement for the tests prescribed so far.
"Companies are hoping for rapid progress and support from animal welfare organisations."