Three new halogenated indole-imidazole alkaloids, securamines E (1), F (2), and G (3), have been isolated from the marine bryozoan Securiflustra securifrons. Their structures were determined by NMR and mass spectrometry. The new alkaloids, 1-3, can all be related to the earlier reported securamine C (4). Compound 1 has an additional bromine substituent at the indole ring system compared to 4; 2 and 4 are diastereomers differing in configuration at one of the four asymmetric carbon atoms; and 3 is a hydrogenated form of 4.