Histological analyses were carried out on cotton explants, primary and friable calli and embryos obtained through somatic embryogenesis. Explants maintained on callus induction medium CIM (basal Murashige and Skoog containing 2,4-D and kinetin at 0.1 mg/l each) gave rise to calli containing differentiated cells with a very large vacuole, and undifferentiated cells, some of them divided with a high nucleo-cytoplasmic ratio. After 7 weeks of culture, few cells under division were seen and the quantity of soluble proteins decreased, suggesting that the activity of these cells was slowing down. This state is maintained until the calli were transferred onto growth regulator-free medium.