Recently, an unknown disease, 'sudden death', in calves has been found in Japanese beef production farms. A previous study conducted by Taira and Ura indicated that sudden death can be effected in calves by hyperinfection of Strongyloides papillosus (SPL) and that the disease is possibly caused by SPL infection. In the present work, an experimental infection of SPL in calves was conducted to confirm the field occurrence. Fifteen Holstein Friesian calves, ranging from 45.5 to 85.6 kg in body weight, were divided into six groups. Calves of Groups A, B, C, D, E and F were infected once at the rate of 100,000, 320,000, 1,000,000, 3,200,000, 10,000,000 and 32,000,000 SPL larvae per 100 kg of body weight, respectively. Five calves were assigned to Group B, while two calves were assigned to the other groups. After showing no premonitory signs, sudden death of ten calves took place. The survival time of these calves was 27.4 and 16.8 days (Group B), 14.8 and 14.8 days (Group C), 13.3 and 14.2 days (Group D), 11.0 and 11.1 days (Group E) and 11.6 and 10.8 days (Group F). Three calves of Group B did not exhibit sudden death. The results of this study demonstrate that strongyloidiasis was the cause of sudden death.