52 patients with a clinical diagnosis of verruca plantaris were entered into a randomised study of acyclovir cream versus placebo cream versus liquid nitrogen. 47 completed the initial 8-week assessment period. At first, liquid nitrogen was used as a positive control but after the entry of 33 patients it was discontinued as an initial therapy in order to obtain maximal numbers of patients on the cream treatments. At the end of the 8-week assessment period 5 of 18 (placebo cream), 7 of 18 (acyclovir cream) and 1 of 11 (liquid nitrogen) patients were completely cleared of their plantar warts. Patients who failed to clear on cream or liquid nitrogen treatments after the initial assessment period but who wished to continue therapy were subsequently treated with liquid nitrogen. Of a total of 27 patients treated vigorously with liquid nitrogen, for periods of time ranging from 2 to 34 weeks, only 11 were completely cleared of their warts at the end of the study. It is concluded that liquid nitrogen should not be considered as a routine treatment for plantar warts and that acyclovir cream is no better than placebo in the treatment of this condition.