Laboratory decay tests were performed on samples of In (Dipterocarpus tuberculatus Roxb.) and Kanyin (Dipterocarpus alatus Roxb. and Dipterocarpus turbinatus Gaertn f.) pressure treated with three wood preservatives - copper arsenic additive (CAA - a variation of ammoniacal copper arsenate), Arquad C-33 (a waterborne quaternary ammonium formulation), and tributyltin acetate (TBTA) dissolved in ethanol. Pressure treatments with each preservative involved a 0.5 - 1 hour vacuum followed by a 4 hour period of pressure. This resulted in a very variable treatment because of the inherent difficulty in treating these woods. The decay tests entailed a slightly modified form of the AWPA M10-77 standard soil-block test using three brown-rot and three white-rot fungi. The untreated In and Kanyin samples were moderately susceptible to decay though weight losses were very variable and some samples of Kanyin (usually the densest and least permeable) were naturally resistant. At the concentrations tested CAA was the most effective in reducing weight losses incurred in the soil-block tests. TBTA was successful in controlling decay caused by all but two of the test fungi. It is suggested that preservative retentions for TBTA conforming to those included in the Candadian standard for bis (tributyltin) oxide would exceed the toxic limit for all the fungi tested

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