The frequency and nature of the oculocardiac reflex and its prevention by atropine or glycopyrrolate (i.m. and i.v.) has been studied in 160 children undergoing surgery for the correction of squint. Ninety per cent of those given no anticholinergic premedication exhibited the reflex. This was decreased to about 50% in those receiving the drugs i.m. Glycopyrrolate 7.5 micrograms kg-1 and atropine 15 micrograms kg-1 i.v. were effective in most instances, the latter being slightly better. However, glycopyrrolate was associated with tachycardia of smaller magnitude. The reflex was observed more often following traction on the medial rectus muscle.