The fine-thread method: lacrimation test for measuring ocular side-effects of drugs in the rat.

Tear production was measured by means of the fine-cotton-thread method in rats. Sedation with hypnorm had no pharmacological effect on normal tear production. Daily oral administration of atropine which was comparable with the dose used for human adults on a drug-to-weight basis, resulted in a 60-percent reduction of tearing. Tearing returned to base-line levels after withdrawal of atropine.