Simultaneous involvement of bands 8p11 and 16p13 in a primary, even though rare, chromosomal translocation recently described in acute nonlymphocytic leukemia may be of crucial interest in some subtypes of this acute leukemia, particularly in the monocytic form. In the present report we describe this translocation in acute nonlymphoblastic leukemia FAB M4, possibly secondary to Hodgkin's disease, though it is also possible that the leukemia may have developed de novo. The aberration t(8;16)(p11;p13) was present in 100% of direct and cultured bone marrow cell preparations. A very high frequency of cells with nonclonal structural chromosome aberrations was also observed in peripheral blood cultures (more than 53%). Random translocations and deletions constituted most of the observed alterations. These findings are discussed with regard to the relationships between secondary leukemias and intensive polychemotherapeutic treatments of primary neoplasias.