A pilot project to evaluate trichlorfon and acephate for suppressing western spruce budworm populations was conducted on the Helena National Forest, Montana. Both insecticides were applied at 1 pound active ingredient per acre. Application was made with a Bell 205A helicopter using eight Beecomist Model 350 spray heads. Treatments and controls were replicated three times. Each replicate covered approximately 1,000 acres. Treatments were applied under a population reduction strategy. The effects of treatments on fish and aquatic organisms and budworm parasites were monitored. Covariance analysis of budworm larval populations 10 days after spraying showed that trichlorfon and acephate gave 59.53 and 86.86 percent control respectively. The degree of foliage protection was estimated at 13.67 percent for trichlorfon and 11.80 percent for acephate. Treatments did not have a significant effect on budworm parasites, fish, or aquatic organisms.