The mRNA expression of protein kinase C (PKC) isozymes (alpha, beta, gamma, delta, epsilon and zeta) in the rat nervous system was investigated with in situ hybridization histochemistry. In the central nervous system of rat, each PKC isozyme mRNAs was expressed in isozyme-specific pattern. PKC alpha mRNA was highly expressed in the olfactory bulb, piriform cortex, hippocampus, substantia nigra compacta, and inferior olive. The expression of PKC beta was highest in the olfactory tubercle, piriform cortex, caudate putamen, accumbens nucleus, neocortex, hippocampus, basolateral amygdaloid nucleus, pontine nucleus, and cerebellum. PKC gamma mRNA was distributed in the caudate putamen, hippocampus and cerebellum and PKC delta was expressed in the thalamus. PKC epsilon had widespread distribution, with relatively high levels in the anterior olfactory nucleus, olfactory tubercle, tinea tecta, piriform cortex, dorsal lateral septal nucleus, neocortex, hippocampus and cerebellum. PKC zeta had widespread and low expression. The spacially differential expression of PKC isozymes (alpha, beta, gamma, delta, epsilon and zeta) suggests that each PKC isozyme may be related with specific cellular function in the nervous system.