In this prospective study, microdrops (mean drop volume 5.6 mu l) and commercially available standard drops (mean drop volume 35.4 mu l) of cyclopentolate, phenylephrine and tropicamide's clinical efficacy and systemic side effects were compared. Sixty-one infants requiring diagnostic pupil dilatation were studied for pupillary diameter, systemic blood pressure, heart rate and skin flushing changes related to the instillation of mydriatic drops. Both microdrops and standard drops of the drugs produced significant increase in pupillary diameter compared with the baseline (p < 0.01). In cyclopentolate and phenylephrine groups, there was no significant pupillary diameter changes between microdrops and standard drops (p > 0.05). Mean blood pressure increased significantly in infants given standard drops. There was no significant change in the group that was given microdrops. In our opinion, reduced volume of mydriatics can prevent possible side effects.