Peroxisomes were purified from the nervous tissue of 14-day-old rats by means of a Nycodenz gradient. Peroxisomal enzymes exhibited different sedimentation patterns: dihydroxyacetone phosphate acyl-transferase equilibrates at 1.142 g/ml together with the first peak of catalase; palmitoyl-CoA oxidase and D-amino acid oxidase activities are mainly recovered at 1.154 g/ml; the second peak of catalase is found at 1.175 g/ml. Morphological and semi-quantitative analyses of immunogold-labelled peroxisomes reveal profound heterogeneity of the particles. Very small (=0.2 microm diameter), electron dense vesicles containing catalase or thiolase, but devoid of other tested enzymes, are preferentially found in the light region, together with larger ( > 0.2 < 0.3 microm) and less electron dense palmitoyl-CoA oxidase-positive peroxisomes. At intermediate density (1.154 g/ml) peroxisomes of more uniform size (0.25-0.27 microm), containing palmitoyl-CoA oxidase or thiolase with or without catalase are preferentially found. This population extends toward the densest region of the gradient, where very large D-amino acid oxidase-containing peroxisomes are also found. In this region, smaller peroxisomes, often polymorphic, which are catalase- and thiolase-positive and D-amino acid oxidase/palmitoyl-CoA oxidase-negative, are also observed. The possibility that the heterogeneity of neural peroxisomes may reflect both cellular heterogeneity and ongoing peroxisomal biogenesis is discussed.