3 Methylcholanthrene induces, in an established cell line from normal mouse kidney cortex, heritable changes with respect to parameters like clonal size and morphology, aptitude for growth in agar culture, piling up with random arrangement (loss of contact inhibition), life span and resistance to the carcinogen. Aptitude for growth in agar, piling up with random arrangement and life span appear to be associated parameters in these variants. Alteration affecting the phenotypic character contact inhibition appears to owe its origin to multiple factors.