BACKGROUND Acitretin has replaced etretinate in the treatment of various disorders of keratinization due to a considerably shorter terminal half-life. Possible esterification of acitretin to etretinate in the presence of ethanol has been reported. OBJECTIVE To determine the plasma concentrations of etretinate as a metabolite in patients with various disorders of keratinization after multiple acitretin dosing, and to assess the influence of alcohol consumption using a questionnaire. In addition, to study the influence of alcohol consumption on the risk of metabolic formation of etretinate. METHODS Eighty-six acitretin (Neotigason(R), Roche)-treated outpatients from three centres provided pre-dose (trough) samples for determining plasma concentrations of acitretin and its metabolites 13-cis-acitretin and etretinate. Patients received acitretin doses of between 0.1 and 1.3 mg kg-1 daily. The concentrations of etretinate, acitretin and 13-cis-acitretin were determined by reverse-phase high-performance liquid chromatography. RESULTS Of the 86 patients, 30 had detectable plasma etretinate levels. No etretinate was found in 20 patients who reported that they never drank alcohol, while etretinate was found in all 16 patients with an average weekly alcohol consumption of > 200 g ethanol, corresponding to about 15 U (1 U equals half a pint of standard beer or a wine glass of non-fortified wine). Etretinate was detected in 14 of 50 patients with a moderate weekly alcohol intake of up to 200 g ethanol. A trend linking higher alcohol intake with both higher risk of etretinate formation and higher etretinate levels was observed. The study also revealed that the ethylesterification only relates to acitretin (13-trans-) and not to the main metabolite 13-cis-acitretin, although the latter compound showed higher plasma trough concentration levels at steady state. CONCLUSIONS Owing to the teratogenic potential and possible side-effects of oral retinoids, fertile women especially should be informed about the importance of strict alcohol abstinence during treatment and for at least 2 months after stopping therapy. In case of non-compliance with alcohol abstinence a post-therapy contraceptive period of 2-3 years should be recommended.