The authors present interim results of a prospective, random assignment, double-blind, placebo-controlled trial conducted to determine whether clonazepam is as effective as alprazolam in reducing the frequency of panic attacks and whether both agents are superior to placebo. Analysis on 44 of 60 randomized subjects showed no statistically significant differences between the clonazepam and alprazolam groups on the following clinically meaningful outcome measures: total number of panic attacks and percent of time subjects experienced anticipatory anxiety, extent of phobic avoidance, and fear. Statistically significant differences did exist among the drug and placebo groups on these measures. The authors conclude that this interim analysis of the data supports the inclusion of clonazepam in the treatment of panic disorder.