Using 6 healthy adult male volunteers, who were divided in halves, the serum and urinary levels of cephaloridine were determined during and after 2-hour constant drip infusion of 2 g cephaloridine dissolved in 500 ml physiological saline solution (= Group I) and 1-hour constant drip infusion of 1.5 g solution (= Group II); besides, pharmacokinetic analysis was made for one-compartment and two-compartment models. On the basis of the values of serum levels obtained from this trial, pharmacokinetic parameters were calculated and simulation curves of serum levels for various doses (0.5 approximately 2 g) and duration (1 approximately 4 hours) of cephaloridine drip infusion were drawn.