The efficacy of Cocois Ointment, a standardized formulation of ung cocois co, in the treatment of moderate to severe scalp psoriasis was assessed in two stages: an open pilot study in 22 adult patients, and a multicentre single-blind randomized comparative study against a coal tar shampoo (Polytar) in 36 patients. In the comparative study, patients whose clinical assessment had failed to improve by more than 50% after 2 weeks were crossed over to the alternative treatment for a further 2 weeks. The proportion of patients showing improvement in the open-label study was highly significant (P0.001; 95% confidence interval 0.77–1). In the comparative study, Cocois was significantly more effective than Polytar in removing scale (P= 0.01). The difference between the two treatments for erythema and plaque infiltration showed a trend in favour of Cocois, but this was not statistically significant. Overall assessment of treatment response showed that Cocois was superior to Polytar in both investigator and patient assessment. These results provide useful contemporary evidence on the efficacy of a traditional remedy, ung cocois co, in the treatment of psoriasis of the scalp.