Four new alkaloids, pterocellins C−F (1–4), have been isolated from the New Zealand marine bryozoan Pterocella vesiculosa. Structural elucidation was achieved through NMR spectroscopic and mass spectrometric analysis and comparison of spectroscopic data with that of the known compounds pterocellins A and B. The biological activities of 1–4 were assessed in a number of different assay systems and compared with those of pterocellins A and B.