The present study was undertaken to examine the effect of a clinically relevant dose of nimodipine (30 micrograms/kg/h) on the autoregulation of CBF in 12 young healthy volunteers. Mean arterial blood pressure (MABP) was measured intraarterially (i.a.), and changes in cerebral blood flow (CBF) were estimated by the arteriovenous-oxygen [(a-v)O2]-difference method. The lower limit (LL) of CBF autoregulation was calculated by a computerized program and tested for different factors for correction of the PaCO2-induced changes in CBF. MABP was increased by norepinephrine (NE) and decreased by ganglion blockade (trimethaphane camphosulfonas) in combination with lower body negative pressure. The MABP manipulations were performed 1 h after infusion of nimodipine. MABP was reduced by 13 mm Hg (8-15 mm Hg), and CBF was increased by 8% (3-12%) during nimodipine infusion. Autoregulation was preserved in 11 of the 12 volunteers. A CO2-correction factor of 1% CBF/0.1 kPa was used. The LL was 75 mm Hg (71-80 mm Hg) [SE 3 mm Hg (2-4 mm Hg)] and not significantly different from a previous control group of healthy volunteers. No side effects were observed. The present study shows a maintained autoregulation of CBF during nimodipine infusion; however, this could be obtained only by reducing the correction for changes in carbon dioxide to 1%/0.1 kPa from 3%/0.1 kPa, which was used in a similar study in healthy volunteers.