Isolation and characterization of normal and neoplastic colonic epithelial cell populations. The aim of the present study was to characterize rat mucosal colonic cells harvested from the crypt continuum during differentiation and dimethylhydrazine-induced neoplasia. The collection of colonocytes was performed using a modified nonenzymatic isolation procedure based on Ca2+ chelation and gentle mechanical dissociation. Light and electron microscopy histomorphological examinations, [3H]thymidine incorporation studies, and activity gradients of alkaline phosphatase, thymidine kinase, and cytoskeleton-associated protein tyrosine kinase indicated that distinct cell populations were harvested from the various crypt regions in a temporal sequence mirroring their zonal and functional distribution in situ. After dimethylhydrazine administration, marked protein tyrosine kinase activity was noted in colonic cells harvested from upper crypt zones. The misplaced and sustained kinase activity preceded the actual polyp or tumor formation. This observation is consistent with the expansion of colonic proliferative compartments beyond allowable boundaries during the preneoplastic period. Companion studies in human colonic epithelial specimens corroborate the findings observed in normal and transformed murine colonocytes. It is believed that the characterization and manipulation of colonocytes using our in vitro model will provide important clues to the molecular events underlying the differentiation program and carcinogenic process in the colonic cell. 