It is believed that xanthines can inhibit cell proliferation by elevating intracellular cAMP. Therefore, these compounds can be useful in hyperproliferative disorders. Our aim was to assess the efficacy of theophylline, caffeine and dyphylline on 3T3 fibroblast proliferation. 3T3 subconfluent cultures were incubated for 3 days with the xanthine derivatives (1 mM-1 microM). At 1 and 0.1 mM the three derivatives exhibited marked inhibition of fibroblast proliferation. Theophylline and caffeine were more potent than dyphylline. At a concentration of 1 mM, the three xanthine derivatives also inhibited proliferation of psoriatic dermal fibroblast, albeit to a lower extent. Caffeine was the most active compound followed by theophylline and dyphylline. We conclude that xanthine derivatives are good candidates for use as fibroblast antiproliferative drugs. We also conclude that 3T3 fibroblasts appear to be a valid system for the pharmacological screening of fibroblast antiproliferative drugs.