We observed 48 patients for 7-21 months (mean, 18 months) after pterygium excision and 2 weeks of placebo or mitomycin topical therapy to evaluate whether or not the short-term efficacy of mitomycin in preventing pterygium recurrence would be reflected in long-lasting efficacy as well. Placebo-treated pterygia showed a 73% recurrence rate. One of 58 (1.7%) mitomycin-treated pterygia recurred (p less than 0.05). We also performed a pilot study comparing pterygia treated with excision followed by 0.4 mg/ml of mitomycin to pterygia treated with excision coupled with conjunctival autograft transplantation to estimate the number of patients required for a randomized clinical trial comparing these two treatment modalities and thereby to decide whether or not such a study would be justified. Thirteen primary and two recurrent pterygia were treated with mitomycin, while 14 primary and one recurrent pterygia were treated with conjunctival autograft transplantation. With mean follow-up times of 4 and 6 months, respectively, no recurrences were noted in the mitomycin-treated group, while the conjunctival autograft transplantation group had one recurrence (6.6%). We estimate that 400 patients would be required for a properly designed clinical trial comparing these two effective therapies for prevention of recurrent pterygia. We conclude that such a study is unjustified, and further conclude that the vastly less expensive, simple therapy of mitomycin eye drops is the more appropriate treatment.