No differences have been found between D‐(—)‐, L‐(+)‐ and DL‐(±)‐prilocaine (citanest®) with regard to intravenous LD50's in mice, nor have any differences been found between the D‐(—)‐ and L‐(+)‐forms on subcutaneous injection. Compared to L‐(+)‐prilocaine, D‐(—)‐prilocaine was less toxic on intravenous infusion (mice, 0.12–0.30 mg/min.) and had less cumulative effect in rabbits (20 mg/kg each 15 min.). The plasma concentrations (cats) of the D‐(—)‐form (25 mg/kg intravenously) were lower than those of the L‐(+)‐form and moreo‐toluidine, one of the metabolites of prilocaine, was detected in the blood. D‐(—)‐prilocaine also produced methaemoglobinaemia at a more rapid rate. The14C‐labelled enantiomers of prilocaine were hydrolyzed at significantly different rates by liver homogenates, slices (mice, rabbits, cats) and isolated microsomes (rabbits); D‐(—)‐prilocaine had the highest affinity for the enzyme(s). Thus, a significant stereospecificity of the hydrolyzing enzymes in their reaction with the enantiomers of prilocaine was found. However, no evidence was obtained which could suggest substitution of th