SUMMARY (1) The hypothesis that rates of food consumption by marine mammals are similar to those of terrestrial mammals was tested by comparing rates of food consumption of nongrowing and growing, juvenile and adult pinnipeds (Carnivora: Caniformia) and whales (Cetacea) to terrestrial Carnivora of known mass. (2) Daily maintenance rates of energy ingestion for adult pinnipeds were not significantly different from those of adult terrestrial carnivores but were about 28% lower than those of terrestrial carnivores with the mustelids excluded. Apparent differences in energy requirements of phocid and otariid seals appeared to result from differences in activity among the experimental animals available for comparison. Data on energy required by cetaceans for maintenance were not available. (3) Among pinnipeds, there was no significant difference in the rates of energy ingested by growing juvenile phocid seals and growing juvenile otariids. Growing juvenile phocids ingested about 1 38 times more energy than juvenile phocid seals at maintenance. The latter required about 1-40 times more energy for maintenance than adult phocids of similar size. (4) The rate of energy ingestion by growing juvenile pinnipeds was relatively higher than for the juvenile terrestrial carnivores sampled. This result appears to arise from differences in body masses and growth rates represented by the two samples rather than from any fundamental differences between juvenile pinnipeds and terrestrial carnivores. (5) Rate of biomass consumption, although frequently used as a measure of food consumption, is not particularly appropriate in comparative studies because it neglects differences in the energy content of food. Nonetheless, the 95% confidence region for rates of biomass ingestion in relation to body mass in marine mammals (seals and whales) included most of the estimates for biomass ingestion rates of terrestrial carnivores held in