The pharmacokinetics of perrimustine and cystemustine, 2 novel 2-chloroethylnitrosoureas (CENUs), were investigated in patients with various cancer diseases. The unique protocol followed in this study consisted of a 15-minute intravenous (IV) perfusion of a 45 mg/m2dose of perrimustine every 4 weeks and a 60 or 90 mg/m2dose of cystemustine every 2 weeks. A sensitive and specific method was developed using solid phase extraction and HPLC analysis, which allowed measurement of the drug concentration levels until at least 3 hours after the beginning of administration of the injection. The rate of disappearance of the 2 drugs from the blood was fitted to either a monoexponential or a biexponential model. When detected, the half-lives of the distribution phase were less than 10 minutes. Regardless of the pharmacokinetic model used, the elimination half-lives were about 50 minutes. The interindividual variations of the pharmacokinetic parameters, as reflected by the variation coefficients (10 to 47%), were lower than those reported in the literature for this class of unstable anticancer drugs. The procedure described here allows one to safely conduct perrimustine and cystemustine pharmacokinetic studies with the purpose of further investigation in a greater number of patients to determine whether any correlation exists between pharmacokinetics, efficacy and/or toxicity.