Abstract:P2protein, a myelin‐specific protein, was detected immunocyto‐chemically and biochemically in rabbit central nervous system (CNS) myelin. P2protein was synthesized by rabbit oligodendrocytes and was present in varying amounts throughout the rabbit CNS. Comparison of P2and myelin basic protein (MBP) stained sections revealed that P2antiserum did not stain all myelin sheaths within the rabbit CNS. The proportion of myelin sheaths stained by P2antiserum and the amount of P2detected biochemically were greater in more caudal regions of the rabbit CNS. The highest concentration of P2protein was found in rabbit spinal cord myelin, where P2antiserum stained the majority of myelin sheaths. P2protein was barely detectable biochemically in myelin isolated from frontal cortex, and in sections of frontal cortex only occasional myelin sheaths reacted with P2antiserum. These results suggest that the regional variations in the amount of P2protein are due to regional differences in the number of myelin sheaths that contain P2protein. P2protein was detected immunocytochemically and biochemically in rabbit sciatic nerve myelin. Immunocytochemically, P2antiserum only stained a portion of the myelin sheaths present. The myelin sheaths not reacting with P2antiserum had small diameters and represented less than 10% of the total myelinated fib