The therapeutic efficacy and acceptability of three scalp shampoo treatments and a placebo shampoo preparation were compared in two similar double-blind clinical studies in a total of 274 patients with dandruff/seborrhoeic dermatitis. In the first study, a shampoo containing 4.0% w/w coal tar BP (Tarmed™) was compared with placebo (shampoo base without coal tar). In the second study, shampoos containing 4.0% w/w coal tar BP plus 1.0% w/w ciclopirox olamine (Tarmed™ AF) or 2.0% w/w ketoconazole (Nizoral™) were compared with a placebo shampoo base without coal tar, ciclopirox olamine or ketoconazole. The placebo formulations used in the two studies were identical. In both studies, unmedicated shampoo was used for 2 weeks (pretreatment washout phase), followed by scalp treatment for 4 weeks, then unmedicated shampoo for a further 2 weeks (regression period). Shampooing was carried out twice-weekly throughout, in accordance with the manufacturers' instructions. Clinical examinations were performed prior to treatment (day 1) and on days 8, 15, 29 and 43. Subjective assessments of efficacy and acceptability were recorded by patients on days 1, 8, 15, 29 and 43. The coal tar plus ciclopirox olamine shampoo and the ketoconazole shampoo produced significant improvements in dandruff and seborrhoeic dermatitis during the treatment phase of the study. The improvements were similar for both treatments, except on day 29, when the coal tar plus ciclopirox olamine shampoo was associated with a significantly greater reduction in the area of seborrhoeic dermatitis than the ketoconazole shampoo. In general, the coal tar shampoo containing only coal tar appeared less effective than the other medicated shampoos. Improvements were sustained during the regression period in the treatment groups, the mean scores on day 43 for the medicated shampoos were significantly improved relative to baseline scores for most of the efficacy criteria.