Recently, resolution of cyclosporine A (CSA)-induced gingival hyperplasia was reported with antibiotic treatment. We therefore assessed the oral status of 45 children on CSA after renal transplantation and evaluated the effects of metronidazole treatment in children with high-grade gingival hyperplasia. Gingival hyperplasia was absent in 19 (42%), mild in 5 (11%), moderate in 13 (29%), and severe in 8 (18%) children. There was no significantly different incidence in high-grade gingival hyperplasia (moderate and severe) between children with (16 of 30) or without (5 of 15) concomitant treatment with calcium channel blockers. The mean trough level of CSA was not different between children with varying severities of gingival hyperplasia. We treated 13 children with high-grade CSA-induced gingival hyperplasia (9 boys, 4 girls, mean age 14.2 +/- 3.4 years) with 750 mg metronidazole in three divided doses (10-25 mg/kg) for a total of 7 days. All 13 children were concomitantly treated with calcium channel blockers for hypertension; their mean monoclonal CSA trough level was 246 +/- 34 ng/ml. Oral examination and photographic documentation were performed by the same examiner on all patients before and 1 and 3 months after metronidazole treatment. We found no changes in gingival hyperplasia; gingival inflammation improved in 5 children (P = ns). We conclude that synergistic effects of calcium channel blockers and high concentrations of CSA in our population may outweigh beneficial effects of metronidazole treatment of CSA-induced gingival hyperplasia after renal transplantation.