The ability of heartwood extracts of two very durable tropical hardwood species (Milicia excelsa (Welw.) C.C. Berg. Syn Chlorophora excelsa (Welw.) and Erythrophelum suaveolens (Guill. & Perr.) Brenan Syn Erythrophleum guinensis) to suppress attack by Lenzites trabea (a brown rotter) or by Polyporous versicolor (a white rotter) was investigated. Air dry extracts were dissolved in 60%, methanol and impregnated into sapwood blocks of Ceiba pentandra Gaertn. Extract dosages were 8.009, 24.778, 48.056 and 96.11 kg/m(3) (0.5, 1.5, 3.0 and 6.0 lb/ft(3)). Treated blocks were exposed to L. trabea and P. versicolor attack for 14 weeks by the soil block method using the procedure set out in ASTM D 1413-72. Only extract dosages of 48.056 and 96.11 kg/m(3) (3.0 and 6.0 lb/ft(3)) were found efficacious in suppressing fungal attack. A tukey studentized test found both dosages significant at 1% level.