Field trials for control of Japanese pine sawyer (Monochamus alternatus) larvae infesting pine logs were conducted in 1987 with the entomopathogenic nematode, Steinernema carpocapsae (str. Mexican). Differences in spray volume and application timing and rate were investigated. The upper surface of horizontally placed logs was applied with 20 million infective juveniles/m² in a spray volume of 300, 600 or 1, 200 ml/m². The 600 ml/m² rate resulted in the highest larval mortality. Nematodes were applied on three different dates, March 17, 30 and April 17 with the highest mortality of Japanese pine sawyer larvae being recorded for the April 17 application. This is attributed to the ambient air temperatures being above 12°C during the treatment. At the April 17 application, rates of 6×10⁶ and 12×10⁶ nematodes/m² showed 69.2 and 72.2% mortality of larvae within the logs. Steinernema carpocapsae appears to be an effective alternative to the chemical insecticide, fenitrothion, for treatment of pine logs infested with the pine sawyer larvae. However, this nematodes can not prevent the spread of pine wilt disease and integrated approach for pine sawyer suppression will still be needed. Jpn. J. Nematol. 23: 71-78 (1993).