Protein kinase C of normal and ras-transformed NIH 3T3 cells was purified by chromatography on TSK DEAE-5PW, threonine-Sepharose, and TSK phenyl-5PW columns. Comparison of the fibroblast enzyme with several types of rat brain protein kinase C by chromatography on a hydroxyapatite column and by immunoblotting, indicates that both normal and transformed fibroblasts possess only one of the four subspecies of protein kinase C which have been identified in brain tissues. This subspecies presumably has the structure encoded by alpha-sequence or a closely related sequence. No significant difference was seen between those enzymes purified from normal and transformed fibroblasts.