The spatial distribution of microfilaments during the first phases of gastrulation in theDrosophila melanogasterembryo was observed in whole mounts using rhodamine‐labelled phalloidin (Rh‐phalloidin). At the beginning of gastrulation, bright fluorescence lined the bases of the blastoderm cells. Fluorescence was most marked at the apices of the cells which constitute the cephalic and ventral furrows. At this time no fluorescence was observed at the bases of the anterior and posterior blastoderm cells. Very bright staining was observed at the apices of the cells constituting the wall of the forming amnio‐proctodeal invagination. The possible relationship between microfilament distribution and gastrulation inDrosophilais also discussed.