1. The pharmacokinetics of dextropropoxyphene (D) and nordextropropoxyphene (ND) have been studied in 12 healthy young (21-28 years) and 12 healthy elderly (70-79 years) male and female subjects. Each received 65 mg D and plasma D and ND concentrations were measured by h.p.l.c. with electrochemical detection for up to 7 days and again after 65 mg D, 3 times daily for 1 week. 2. There were no significant differences in median D and ND half-life, AUC, Cmax and tmax between the male and female subjects in either group. Within the groups the mean D half-life (h) was longer in the young after multiple dosing (mean +/- s.d.:13.2 +/- 5.2 and 23.7 +/- 11.3, P less than 0.05, paired t-test) but there were no other significant differences. 3. Between the groups, the median single and multiple dose D and ND half-lives were all significantly longer (P less than 0.02) and the median D AUC for both single and multiple doses was significantly higher (P less than 0.01 and P less than 0.05, respectively, Mann-Whitney U-tests) in the elderly. 4. There was no relation between multiple dose Cmax and other parameters such as single dose D half-life. However, across the groups D and ND half-lives after both single and multiple dosage correlated significantly with estimated creatinine clearance, the correlation being strongest with ND (r = -0.76 and -0.84, respectively).