Parvalbumin is supposed to function as an intracellular Ca2+ buffer in the brain, but its concentration in nerve cells is unknown. We combined radioimmunoassay of parvalbumin in rat brain extracts, together with image analysis of area fractions immunostained with the parvalbumin antibody on sections, to deduce the intracellular concentration of parvalbumin. We found that the average amount of parvalbumin varied between 6 microM in the caudatoputamen and 45 microM in the cerebellum. Although these values are only rough averages and do not demonstrate a Ca2+ buffering role for parvalbumin in neurons, the concentration of the protein is at least in the appropriate range for such a function.