The pharmacokinetic profile of 0.2 mg kg-1 midazolam given i.v., for induction of anaesthesia, was compared in young subjects and in those who were over 80 years of age. Thirty-five patients were allocated into four groups according to their sex and age. Plasma samples were drawn before midazolam injection and at regular intervals over 24 h following injection. Plasma midazolam concentrations were measured by electron capture gas-liquid chromatography. Equilibrium dialysis was used to assess the plasma protein binding of midazolam. Distribution volume (Vdss) was significantly increased in elderly subjects when compared to young subjects of the same sex (young vs. elderly males, Vdss = 1.22 +/- 0.31 l kg-1 and 2.47 +/- 0.98 l kg-1 respectively; and young vs. elderly females, Vdss = 0.91 +/- 0.29 l kg-1 and 1.70 +/- 0.78 l kg-1 respectively). Total body clearance was significantly reduced in elderly males compared with young males (5.60 +/- 1.77 ml min-1 kg-1 vs. 8.10 +/- 3.58 ml min-1 kg-1). No significant difference in clearance was found between young and elderly females (6.08 +/- 2.04 ml min-1 kg-1 vs. 9.14 +/- 3.36 ml min-1 kg-1). As a consequence, elimination half-life (T1/2E) was significantly prolonged in elderly compared to young males (8.52 +/- 5.4 h vs. 2.77 +/- 0.80 h). In contrast, T1/2E was unchanged in elderly compared to young females (2.99 +/- 0.86 h vs. 2.86 +/- 1.04 h). Midazolam plasma protein binding was not influenced by age and sex.