Mitogenic effect on Balb/c 3T3 cells of the HB-EGF molecule released by the ML-3 cell line and by ex vivo myeloid blasts. ML-3 and AML blasts were stimulated with PMA to induce both new transcripts and release of HB-EGF (see text). Results were expressed as percentage increase in Balb/c 3T3 cell number versus untreated controls ± SD (P < .01). Each test was replicated five times.