The CFU-GM (granulo-macrophagic colony forming unit) content of 130 bone marrow samples and 105 cytapheresis blood samples was evaluated by two culture techniques, one in agar with human placenta conditioned medium as stimulating factor, the second in methyl cellulose with a cocktail of recombinant G-CSF, GM-CSF, IL-3 and erythropoietin as stimulating factors. The aim of the study was to evaluate in methyl cellulose the CFU-GM threshold doses necessary to ensure hemopoietic reconstitution in autologous transplantation that we previously determined in the agar technique. Thirty-one out of the 130 BM samples were also tested after incubation with mafosfamide, and 33 after freezing and thawing. Results showed that the numbers of CFU-GM in the 2 techniques were significantly correlated (p < 0.0001). The strongest correlation was found with the formula "log CFU-GM methyl = a log CFU-GM agar + b" with a slight variation in the values of a and b among the 4 settings, i.e. unmanipulated BM, mafosfamide-treated BM, frozen-thawed BM and unmanipulated blood samples. According to the formulas, the threshold doses of CFU-GM for BM and blood, previously determined in the agar technique (respectively 10(4)/kg and 5 x 10(4)/kg) were calculated for CFU-GM grown in methyl and corresponded respectively to 2.3 x 10(4)/kg and 2.1 x 10(5)/kg.