In this paper, we have analysed cells which are in the process of enucleation in mouse spleen. We have provided additional support for the hypothesis that erythroid cells can autonomously undergo enucleation. The presence of a constriction in the nucleus and in the plasma membrane during this process has bee confirmed. Microfilaments have been described for the first time in the cytoplasm of maturing erythroid cells. Their position during enucleation is suggestive of an active role for these elements in this process.