Pharmacokinetics of a number of drugs are altered in the elderly (Crooks, O'Malley & Stevenson, 1976). A reduction in digoxin excretion related to decreased renal function has been shown in the elderly (Ewy, Kapadia, Yao, Lullin & Marcus, 1969) and is an important determinant of added susceptibility to unwanted effects of this drug. Alterations in absorption or distribution of digoxin would also affect dose requirements in these patients. In this study we compared digoxin pharmacokinetics in elderly and younger patients with particular emphasis on absorption and distribution. Observations were made in seven elderly (aged 72-91 years) and six younger (aged 34-61 years) patients, in whom digoxin was indicated for its inotropic effect. Elderly patients received digoxin 0.25 mg and younger patients digoxin 0.5 mg R.J.P. (PROC.) A both intravenously and orally with at least 2 weeks between doses. Blood samples for estimation of plasma digoxin concentrations by radioimmunoassay were withdrawn before, at 15, 30, 45 and 60min and at 1.5, 2, 2.5, 3, 3.5, 4, 5, 6, 7, 8, 12, 24, 36 and 48 h after administration of digoxin.The results are shown in Table 1. Peak digoxin concentrations were attained earlier in the younger subjects (P < 0.05, Wilcoxon's rank sum test). Digoxin half-life after both routes was significantly longer in the elderly. The extent of absorption calculated as the ratio of area under the plasma concentration-time curves after oral and intravenous administration was not significantly different in the young and old subjects. The elderly had a significantly smaller apparent volume of distribution but after correction for weight the difference was not significant. Plasma clearance of digoxin (both absolute and weight corrected) was significantly lower in the older patients.Thus the rate of absorption of digoxin is slowed in elderly patients but the extent of absorption is unchanged. Older patients have a smaller volume of distribution of digoxin which probably reflects their decreased lean body mass.