Chlorpyrifos, a soil insecticide reported to have activity in controlling southern stem rot of peanuts, was evaluated in an area heavily infested with the southern stem rot pathogen Sclerotium rolfsii Sacc. over a three year period (1981-1983). Chlorpyrifos 4E at 0, 1.12 or 2.24 kg ai/ha was applied preplant incorporated broadcast followed by 0, 1.12 or 2.24 kg ai/ha chlorpyrifos 15G or 4E at pegging in a 40 cm band over the row. Combinations of chlorpyrifos and PCNB were also evaluated as a formulated granule and as concomitantly applied separate materials. Disease loci were enumerated during the season and at inverting and yields were determined for plots. Chlorpyrifos alone did not significantly decrease disease in any of the tests over the three year period at any rate or method of application tested. A PCNB + chlorpyrifos (11.2-2.24 kg ai/ha) combination granule and the two chemicals applied concomitantly were as effective as PCNB + fensulfothion (11.2-3.36 kg ai/ha) in reducing disease and increasing yield. Potential niches for the use of chlorpyrifos in reducing southern stem rot are discussed.