Adherent UG3 cells cultured in the presence of M-CSF (100 ng/mL) for 2 weeks. Double staining for a-naphthyl butyrate esterase and naphthol AS-D chloracetate esterase (A; original magnification, 100-fold) and phase-contrast microscopy (B; original magnification, 60-fold). Morphological analysis was performed of cells obtained from two independent cultures.