BACKGROUND: Monitoring of psoralen concentration and time-course in PUVA patients is vital for efficient PUVA therapy. Blood sampling is invasive and labour-intensive and thus unsuited for routine use and repeat measurements over the course of therapy. OBJECTIVE: Psoralen pharmacokinetics in saliva were investigated and validated as a noninvasive, simple and biologically relevant alternative to measurements in blood. METHODS: The time-course of psoralen concentration was measured in saliva and serum of volunteers and patients receiving PUVA or extracorporeal photopheresis therapy. The samples were analysed by high-performance liquid chromatography. Three commonly used oral psoralen preparations were tested: Psoraderm5 (5-methoxypsoralen; 5-MOP), Meladinine and Oxsoralen (both 8-methoxypsoralen; 8-MOP). RESULTS: The pharmacokinetic parameter Cmax in saliva averaged 10% (range 6-20%) of the serum values for 8-MOP, and < or = 4% for 5-MOP. These concentrations correspond to the therapeutically relevant, non-albumin-bound fraction of psoralen in serum that is available to diffuse into the tissues. The parameter tmax in saliva and serum coincided, indicating that psoralens diffuse rapidly between the two compartments. CONCLUSION: Monitoring of psoralens in saliva is a valuable, noninvasive alternative to measurements in serum, suitable for routine use. A series of five or six saliva samples is sufficient to determine tmax in a patient beginning photochemotherapy. To determine Cmax, three independent saliva measurements at t = tmax are recommended.