For routine mydriasis, many clinicians prefer to utilize a combination of adrenergic and anticholinergic agents. Some clinicians, however, omit the adrenergic agent because of a real or perceived fear of inducing adverse systemic side effects. The agent most often implicated in causing side effects is 10% phenylephrine. Although the 2 1/2% concentration rarely results in adverse systemic side effects when applied topically for pupillary dilation, we undertook this study to determine whether another adrenergic agent, 1% hydroxyamphetamine, which lacks the notoriety of phenylephrine, would be equally effective in producing mydriasis.