K562 human leukemia cell line undergoes in vitro terminal differentiation towards the erythroid pathway following treatments with appropriate chemical agents including aclacinomycin, fagaronine and hemin. These three drugs induced a different expression of phenotypic and functional characters associated with differentiation. The morphological characteristics of the differentiation sequences elicited by these agents were evaluated by image analysis using a SAMBA 200 cell image processor. Multivariate statistical analyses of morphological data revealed that only aclacinomycin was able to induce significant modifications of the morphological parameters similar to those observed during the maturation of normal bone-marrow erythroblastic cells. These data correlate with the higher inductive potency of aclacinomycin as compared to hemin or fagaronine and suggest that quantitative cytology may be a useful adjunct to conventional tests for the selection of new drugs with differentiating potential.