Three cases of gingival overgrowth induced by cyclosporin and/or nifedipine have been reported. Patient A was under medication with cyclosporin plus nifedipine, patient B with nifedipine only and patient C with cyclosporin only. The significance of androgen metabolism in gingival tissue with respect to hyperplastic changes has been studied by several workers. Hence, we have investigated whether gingival tissue from the above patients showed significant metabolism of the androgen, testosterone, to its biologically-active form, 5 alpha-dihydrotestosterone (5 alpha-DHT). Radical gingivectomy was carried out in all 3 cases to remove the hyperplastic tissue. The excised tissue was incubated with labelled testosterone in order to study the extent of androgen metabolism. Healthy gingivae from males and females produced 5 alpha-DHT (22.4 +/- 7.7, s.e.m., n = 8). Very significantly higher values (p less than 0.001) were recorded for patients A, B and C (1139, 542 and 994 fmol/mg, respectively). These represented increases of 51-, 24- and 44.4-fold, respectively over control values. Corresponding production of 4-androstenedione from testosterone was 28 +/- 8.3, s.e.m., n = 8, fmol/mg. In patients A, B and C, 4-androstenedione production was elevated: 85, 901 and 113 fmol/mg, respectively, representing increases of 3-, 32- and 4-fold. Even the lower values of 85 and 113 fmol/mg were very highly significant (p less than 0.001) compared with control values. Although healthy female gingival tissue does not metabolize testosterone significantly, in the presence of inflammation the extent of 5 alpha-DHT formation is comparable to that of male samples.(ABSTRACT TRUNCATED AT 250 WORDS)