Procoagulant activity (PCA) was investigated in relation to cell growth, differentiation, and cytogenetics in seven human neuroblastoma cell lines. Before 5-bromodeoxyuridine (BrdUrd) treatment, PCA was notably heterogeneous, with the highest activity in NCG (S-type in morphology) 40- to 100-fold greater than the lowest activity in SK-N-DZ (N-type). PCA was not related to 1p abnormalities. After BrdUrd treatment at 5 micrograms/ml for 6 days, PCA increased 6.8-fold in GOTO and 2.7-fold in SK-N-DZ with associated growth inhibition and morphological changes (I-type morphology converted to S-type in GOTO and N-type converted to an advanced N-type in SK-N-DZ). In contrast, only growth suppression was observed in 2 other cell lines, and no changes in PCA, growth or morphology were induced in the remaining 3 cell lines.