The chemical study of three New Zealand marine organisms is described, along with a survey of the chemistry and biological activity of eighty-five marine organisms collected from New Zealand waters. The study of the New Zealand marine bryozoan Pterocella vesiculosa has resulted in the isolation of three new compounds; pterocellin H, pterocellin I and 1-methyl-5-bromo-8-methoxy-β-carboline. These compounds were characterised using high resolution mass spectrometry, one- and two-dimensional nuclear magnetic resonance spectroscopy and X-ray crystallography. The biological activity of these compounds was investigated and a discussion of the results including a comparison with the activity of closely related compounds is also presented. The crude extracts of eighty-five marine organisms were surveyed to establish their biological activity and chemical constituents. The results of this study indicated which species had interesting biological activity. The chemical survey allowed geographical and intra-species comparisons of chemical constituents between samples, as well as potentially indicating the presence of known secondary metabolites. For the Pterocella vesiculosa samples the survey methodology clearly illustrated the presence of pterocellins A and B. Two marine organisms were chosen for further investigation based on their biological activity and chemical survey results. Bioactivity directed isolation procedures yielded no new compounds from the organisms. The sterol composition of these species is also presented.