AbstractTreatment of cultured rat osteoblasts with staurosporine caused a rapid outgrowth of long slender cellular processes and the formation of stellate cells. The number of stellate cells increased with higher concentrations of and longer incubation with staurosporine. Scanning electron microscopy (SEM) revealed that the smooth surface of control polygonal cells became ruffled with many long slender cellular processes, thus increasing the cell surface area. Transmission electron microscopy (TEM) of the stellate cells showed a rich accumulation of large lipid droplets in the cytoplasm. Some lipid droplets had coalesced under the cytoplasmic membrane. We suggest that staurosporine has an effect on the differentiation of cultured rat osteoblasts.