METHODS Experiments on rabbits. Under nembutal anaesthesia an intercostal space was exposed on the right side through a skin incision. Muscles were retracted to expose the intercostal muscles over a small area. The material to be introduced was then injectedinto the pleural cavityfrom a syringe through a flat bevelled needle. The muscles were replaced, the skinincision sutured and the animal allowed to recover from the anaesthetic, which usually took about 1 hr. Operations were not performed under strict aseptic conditions, but in no case was there evidence of post-operative infection.