Amylobarbitone sodium (200 mg) was given by intravenous injection to nine healthy, young adults (four males). Subjects were drug-free and nonsmokers. Serial blood samples were drawn for 48 h following the infusion, and multiple sample and single sample estimates of clearance were calculated. The mean (+/- s.d.) values for clearance (CL) and apparent volume of distribution (V) were 0.032 (+/- 0.007) 1 h-1 kg-1 and 1.08 (+/- 0.16) 1 kg-1, respectively. The mean (+/- s.d.) single sample estimate of clearance, CL, based on just the 48 h plasma concentrations of amylobarbitone was 0.033 (+/- 0.006) 1 h-1 kg-1. The 48 h single sample CL value was shown to reliably reflect the value of CL with little bias and good precision. Values of the 48 h CL when compared to CL exhibited a mean prediction error (mpe) of 1.2% with 95% confidence limits of -6.3% to 9.4%, and a root mean squared error (rmse) of 9.4%. It is concluded that amylobarbitone's clearance can be estimated in a single dose, single sample protocol permitting its use as a single dose, single sample probe for studying host factor influences on drug metabolism.