The probability of ocular adverse reactions to systemic medication is low but when a reaction does occur it is often associated with one or more special factors relating to the condition being treated, to the patient, and to the nature of the drug itself. Nevertheless the role of the optometrist in the monitoring, detection and reporting of adverse reactions is important and is recognized by the College reporting scheme. A selection of the type of reactions that may be encountered in general optometric practice is reviewed. The reactions range from the relatively innocuous anticholinergic effects of the benzodiazepine tranquillizers to the more serious corneal, lens and retinal changes that may be associated with the corticosteroids, phenothiazines and chloroquine.