A retrospective analysis of patients receiving isotretinoin for acne was performed, in order to determine the necessity for routine testing of lipid profiles and liver function tests during therapy. Data were analysed from 209 individuals, 113 (69 males, 44 females) of whom had been treated with 1 mg/kg/day, and 96 (67 males, 29 females) with 0.5 mg/kg/day. There were no significant changes in any of the tests of liver function. There were significant elevations in both plasma cholesterol and triglycerides at 8 and 16 weeks (P < 0.01) for both dose schedules, which were significant in both male and female subjects (P < 0.001). All the individuals with elevated cholesterol (> 6.5 mmol/l) at 16 weeks had elevated cholesterol at the onset of therapy. Triglyceride concentrations were elevated at 8 weeks, but there was no further increase thereafter. It was not possible to predict which subjects would become hypertriglyceridaemic from pretreatment lipid estimations. In conclusion, there appears to be little evidence to support the previously recommended regular biochemical monitoring of liver function and lipid profiles in patients who are treated with isotretinoin for 16 weeks. It would appear prudent to ensure that there is neither liver disease nor hyperlipidaemia prior to the onset of therapy, and to determine the triglyceride response to therapy on one occasion after 4 weeks' treatment. This change in patient management should result in considerable savings both in patient time and in blood collection and analysis.