A sensitive and reliable stripping voltammetric method was developed to determine Cephalothin antibiotic drug. This method is based on the adsorptive accumulation of the drug at a hanging mercury drop electrode and then a negative sweep was initiated, which yield a well defined cathodic peak at -625 mV versus Ag/AgCl reference electrode. To achieve high sensitivity, various experimental and instrumental variables were investigated such as supporting electrolyte, pH, accumulation time and potential, drug concentration, scan rate, convection rate and working electrode area. The monitored adsorptive current was directly proportional to the concentration of Cephalothin and it shows a linear response in the range from 4 x 10(-7) to 1.2 x 10(-6) mol l(-1) (correlation coefficient=0.9995) and the detection limit (S/N=3) is 3.3 x 10(-9) mol l(-1) at an accumulation time of 3 min. The developed AdSV procedure shows a good reproducibility, the relative standard deviation R.S.D.% (n=10) at a concentration level of 5 x 10(-7) mol l(-1) was 0.94%. Possible interferences by other pharmaceutical drugs and surfactants have been also evaluated. The applicability of this approach was illustrated by the determination of Cephalothin in pharmaceutical preparation and biological fluids such as serum and urine.