The present study investigates the relationship between the pharmacokinetic variables of nifedipine with the incidence and severity of gingival overgrowth in 9 adult male patients medicated with the drug for at least 6 months. Five of the patients had experienced significant gingival changes and were thus designated "responders". The remaining four patients exhibited no gingival overgrowth, and thus acted as a control. A baseline periodontal examination (plaque scores, bleeding index and gingival overgrowth assessment) was carried out on each patient, and confined to the upper and lower anterior teeth. Serial blood and gingival crevicular fluid samples were collected over an eight-hour investigation period. Samples were analyzed for nifedipine by gas chromatography. No significant difference (p > 0.05) was seen between responders and non-responders with regard to drug therapy, periodontal parameters or plasma pharmacokinetics of nifedipine. Nifedipine was detected in the gingival crevicular fluid of seven subjects (all responders, and two non-responders). The peak concentration of nifedipine in crevicular fluid was 15-90 fold greater than levels observed in plasma.