The pharmacokinetics and analgesic effect of i.v. ketamine in doses of 125 microgram kg-1 and 250 microgram kg-1 were determined in five healthy volunteers. Analgesia was measured with the submaximal effort tourniquet test. Both doses of ketamine prolonged the period of pain-free ischaemic exercise while the plasma ketamine concentration was greater than 100 ng ml-1. Ketamine was distributed rapidly (T 1/2 alpha = 17 min). The elimination half-life was 186 min.