Reference serum selenium and manganese concentrations were established for healthy nulliparas aged 18-23 years resident in Cape Town. Measurements were determined for selenium in 100 female students who had been taking low-dosage triphasic contraceptive medication for a minimum of 3 months and in 100 female students who were not on contraceptive therapy. Manganese concentrations were determined for 25 female students from each group. The mean serum selenium concentrations were 0.988 +/- 0.189 micrograms/l (78 +/- 15 micrograms/dl) and 0.925 +/- 0.177 mumol/l (73 +/- 14 micrograms/l) respectively for females taking and not taking oral contraceptives. The corresponding concentrations for manganese were 21.84 +/- 9.82 nmol/l (1.20 +/- 0.54 micrograms/l) and 21.66 +/- 7.64 nmol/l (1.19 +/- 0.42 micrograms/l) respectively. The differences in selenium were statistically significant (P = 0.0231) but not for manganese (P = 0.910).