Mycophenolate mofetil (MMF) has been shown to be effective in the treatment of psoriasis. MMF is the morpholinoethyl ester of mycophenolic acid (MPA), the active compound. Our objective was to characterize the pharmacokinetic profile of MPA in patients with psoriasis treated with MMF and to examine its correlation with effectiveness and toxicity. Eleven patients with moderate-to-severe chronic plaque psoriasis were treated with oral MMF 30 mg kg-1 daily over a period of 16 weeks. Patients were reviewed at 3, 8 and 16 weeks, checking the Psoriasis Area and Severity Index (PASI) and possible adverse events, and performing MPA C0 (trough) and C1 (1-hour post-dose) plasma levels. The reduction in PASI was statistically significant in all our patients. The drug was well tolerated. There was no significant correlation between C0 and C1 MPA levels and the reduction of PASI, improvement rates of PASI from baseline, weight of the patients and total dosage of MMF. Nevertheless, the highest detected mean levels of MPA C1 were observed in two of the patients with the highest improvement rate of PASI at the end of the study. Although C1 levels do not seem to strongly correlate with the effectiveness of the drug, the finding that the highest detected mean levels of MPA C1 were observed in two of the patients with the highest improvement rate of PASI suggests that the monitoring of C1 could be useful in some individual cases.