Two additional cytochalasins were isolated from liquid culture filtrates of Phoma exiuua var. heteromorvha together with some already known cytochalasins. The two new metabolites, named cytochalasin U and V, represent the first natural occurrence of a 25,26-dioxa(161 and 2% oxa[lS]cytochalasan, respectively, both bearing a formyl group on the macrocyclic ring. Cytochalasins U and V showed respectively significant and weak activity in the brine shrimp assay.