Studies on the effects of age on the pharmacokinetics of alfentanil are inconclusive. A possible factor in explaining the differences between various studies could be the effect of gender. The authors studied the effects of age on the pharmacokinetics of alfentanil in female (n = 21) and male (n = 15) patients undergoing lower abdominal surgery under nitrous oxide alfentanil anaesthesia. There was a significant negative correlation (r = -0.79, p less than 0.001) between plasma alfentanil clearance (CL) and age in women (less than 50y, median CL 24.84 L/h; greater than 50y, median CL 14.52 L/h), but not in men (less than 50y, median CL 19.44 L/h; greater than 50y, median CL 16.2 L/h). The conclusion is drawn that the effects of age on the pharmacokinetics of alfentanil are gender-dependent.