Samples of archaeological human skeletons from excavations at Afetna, Saipan, were analysed for δ 1 5 N andδ 1 3 C. The marine resources identified in the Afetna site appear to have been derived almost exclusively from the coastal lagoonal environment and the isotope analysis was expected to confirm this interpretation. The proportion of marine resources in the Afetna diet, as indicated by the 1 3 C and 1 5 N values, is greater than has been indicated by traditional faunal analysis, suggesting some exploitation of the open ocean.