The pharmacokinetics of dicloxacillin and flucloxacillin were studied in 12 healthy volunteers after oral administration. The participants received a single dose of either dicloxacillin (0.5 g, 0.75 g or 1.0 g) or flucloxacillin (0.75 g) in a cross-over fashion. Antibiotic concentrations were determined in serum and urine by bioassay and followed for 8 and 24 h, respectively. The three dicloxacillin dosages showed no significant differences for the serum elimination half-lives (t1/2β, median: 72 min). Comparing 0.75 g flucloxacillin with the same dose of dicloxacillin, no significant differences between the values of Cmax, t1/2β and AUC were found. Protein binding as determined by ultrafiltration in pooled serum was 94.7-96.2% for flucloxacillin and 96.4-97.2% for dicloxacillin. The serum bactericidal titers were similar for the two drugs. In conclusion, dicloxacillin and flucloxacillin showed similar pharmacokinetic behavior after 0.75 g doses in human volunteers.