Single-dose and steady state pharmacokinetics of diltiazem administered in two different oral formulations were assessed with particular reference to rate and extent of absorption. Following single dose administration a significant difference in tmax was observed (2.9 +/- 1.9 and 6.8 +/- 2.6 hr respectively) whereas differences in AUC, t1/2 and Cmax were not significant. The AUC (mean +/- S.D.) values following single dose administration of Cardil and Cardizem were 678.4 +/- 321.5 and 948.6 +/- 580.6 ng.ml-1.hr respectively. The mean and the 95% confidence limits for the observed ratio AUCCardil/AUCCardizem are 0.89 and 0.44-1.34 respectively. At steady-state a significant difference between Cmax/Cmin and tmax was seen Cmax/Cmin being 4.9 and 3.2 respectively and Tmax being 2.7 +/- 2.0 and 6.0 +/- 2.8 hr respectively, whereas Cmax and AUC did not differ significantly. The AUC (mean +/- S.D.) values in steady state of Cardil and Cardizem were 880.1 +/- 399.8 and 1056.8 +/- 509.8 ng.ml-1.hr respectively. The mean and the 95% confidence limits for the observed ratio AUCCardil/AUCCardizem are 0.96 and 0.66-1.26 respectively. Although the observed ratios AUCCardil/AUCCardizem in both the single-dose and the steady-state study do not differ significantly from 1.0, the confidence limits exceed the acceptable values given by Poulsen & Juul (personal communication 1990) (a 20% decrease or increase of the ratio to 0.8 or 1.2).