A cytologic and cytogenetic study of 10 cases of acute myeloblastic leukemia with maturation and t(8;21) translocation is reported. Despite a certain polymorphic appearance, the characteristic cytologic picture, consisting essentially of large myeloblasts with an abundant cytoplasma containing a large Auer rod, allowed the presence of the chromosome anomaly to be predicted. t(8;21) translocation was attended by the loss of a sex chromosome in 7 of 10 cases. The comparative study of mitoses using cytologic and cytogenetic techniques showed that cells exhibiting normal karyotypes were essentially erythroblasts. This finding suggests that the chromosome anomaly does not affect all the bone marrow cell lines. After short-term culture, the percentage of normal karyotype mitoses diminished, as did the number of mitoses in erythroblasts.