In two consecutive cross-over studies, each involving 10 healthy volunteers, the pharmacokinetics of (6R,7R)-7-(2-[3,5-dichloro-4-oxo-1(4H)-pyridyl]-acetamindo)-3-([(5-methyl-1,3,4-thiadiazol-2-yl)-thio]methyl)-8-oxo-5-thia-1-azabicyclo[4,2,0]oct-2-ene-2-carboxylic acid (cefazedone, Refosporen) in comparison with cefazolin were investigated after single i.v. and i.m. administration. The doses were: i.v. cefazedone 500 mg and 1000 mg; cefazolin 1000 mg; i.m. cefazedone 500 mg, cefazolin 500 mg. The pharmacokinetic parameters were analysed by applying an open two-compartment model. The pharmacokinetics of cefazedone are nearly identical with those of cefazolin. In particular, it must be noted that cefazedone has a relatively long serum elimination half-life (1.64 +/- 0.23 h after i.v. and 1.85 +/- 0.51 h after i.m. administration) and that cefazedone exhibits, in comparison with cefazolin, a more favourable concentration ratio of central vs. peripheral (= tissue) compartment (1:2).