The current study was undertaken to search for differences in the biology of cytogenetic subgroups in patients with de novo acute myeloid leukemia (AML). In addition, factors influencing the metabolism of cytosine arabinoside (araC) as the key agent of antileukemic activity were assessed. Bone marrow aspirates from 91 patients with newly diagnosed AML in whom karyotypes were successfully obtained were analyzed: (1) for spontaneous proliferative activity by 3H-thymidine (3H-TdR) incorporation; (2) proliferative response to GM-CSF by in vitro incubation of blasts for 48 h with or without GM-CSF (100 U/ml) followed by an additional 4-h exposure to 3H-TdR (0.5 microCi/ml); and (3) parameters of araC metabolism comprising 3H-araC uptake in vitro and the activities of polymerase alpha (poly alpha), deoxycytidine kinase (DCK) and deoxycytidine deaminase (DCD). According to the results of chromosome analyses four cytogenetic subgroups were discriminated: (I) normal karyotypes (n = 38); (II) favorable karyotypes [t8;21), t(15;17), inv(16)] (n = 16); (III) unfavorable karyotypes [inv (3), -5, 5q-, t(6;9), +8, t (9;11), complex abnormalities] (n = 20); (IV) karyotypes of unknown prognostic significance (n = 17). Proliferative activity of leukemic blasts was significantly higher in favorable karyotypes (group II) as compared to cases with unfavorable cytogenetics (group III) with median values and range for 3H-TdR uptake in group II of 2.48 pmol/10(5) cells (0.28-25.8) and in group III of 0.51 pmol/10(5) cells (0.04-7.6) (P = 0.0096). The respective values in group I and group IV were 0.7pmol/10(5) cells (0.0-6.7) and 0.98 pmol/10(5) cells (0.0-4.0), respectively. Inversely, response to GM-CSF, as defined by an increase in 3H-TdR incorporation >1.5- fold over control values after 48h of GM-CSF exposure, was significantly lower for patients with a favorable karyotype (group II) as compared to group I (P = 0.04) and group III (P = 0.013). No significant differences between karyotype groups I, II, III and IV were found for 3H-araC incorporation, nor for the activities of poly alpha, DCK and DCD. These data demonstrate differences in the biology of cytogenetic subgroups in AML which may partly explain the well established differences in clinical outcome.