n 1955 some 3000 Crabeater Seals Lobodon carcinophagus wintered on the sea‐ice of the Crown Prince Gustav Channel. The seals, most of which were young, were ten times more numerous in 1955 than is normal in winter. Most of the animals died in the spring from a contagious disease whose effect was probably increased by crowding and partial starvation. Its exact nature was not elucidated, but a virus infection is likely. The average mortality was 85 per cent but in places the figure was 97 per cent. Although the population was observed before, during and after the normal pupping season, no live births but only abortions were recorded. Some abortions were found three weeks before any adult mortality or any sign of disease. It is unlikely that the epidemic had any appreciable effect on the total number of Crabeater Seals in Antarctica. The disease did not spread to the intermingled Weddell Seals Leptonychotes weddelli; diseased meat was eaten by dogs and by man with no ill effects.