A series of N-substituted isothiazolones was tested in laboratory decay tests for efficacy in controlling some organisms of wood decay, including the brown rot fungus <i>Gloeophyllum trabeum</i> on southern yellow pine sapwood, the white rot fungus <i>Irpex lacteus* 1 on aspen sapwood, <i>Coriolus versicolor</i> on either sweetgum or southern yellow pine sapwood and soft rot fungi. The soft rot fungi were tested by burial of birch blocks in unsterile soil and incubation under conditions that stimulated growth of soft rot fungi from the natural microflora. In general, the isothiazolones were more active against brown and soft rot fungi, than against <i>Irpex lacteus* 1. The most active compound found was N-octyl-4, 5-dichloroisothiazolin-3-one with the N-cyclohexyl analog exhibiting only slightly less activity overall. -- AATA