Drug-induced gingival overgrowth is a disfiguring condition that is a side effect encountered in susceptible responder patients common to three groups of drugs - immunosupressants, calcium channel blockers and anticonvulsant agents. The altered overgrown gingiva can be aesthetically displeasing but in severe cases it can cause functional problems and such patients may eventually require excision of excess tissue. The underlying mechanisms that mediate drug-induced gingival overgrowth is uncertain and the various investigations into the pathogenesis of this disease suggest that it is multifactorial. This study investigated the effects of exogenous addition of cycJosporin and amlodipine on the growth and proliferation of human gingival fibroblasts and the production of collagen by these cells. Results showed that these drugs have a direct stimulatory effect on the gingival fibroblasts of responder patients in vitro and there seems to be a synergistic effect between the two drugs. Findings of this study have important relevance as it suggests that fibroblast proliferation and collagen production must play a significant role in the pathogenesis of drug-induced gingival overgrowth.