Discolourations of hem-fir, usually called hemlock brownstain, have become an economically important problem with the move towards increased kiln-drying of the wood species mixture and added-value products in which discolourations cannot be tolerated. These discolourations, clearly different from sapstain, can occur in several types and intensities and are a serious problem in high-value markets. Because little is known about their causes means for their control are still unavailable. Therefore fundamental research was initiated to elucidate the biology and chemistry of hemlock brownstain and to suggest control measures. A post graduate student was hired to undertake laboratory and field work as part of a Ph.D. program. The thesis subject was "the role of microorganisms in the phenomenon of hemlock brownstain". The thesis covers: a literature review; laboratory work to locate the stain and define its nature; a storage study of logs and lumber to monitor progress in development of brownstain; fungal isolation work and sap characterization studies; in vitro production of hemlock brownstain in wood and sap; and additional laboratory experiments to determine what factors influence the formation of the brownstain. In addition to the thesis research the role of bacteria in the formation of the stain was investigated in the laboratory and the ability of various chemicals, including fumigants, to prevent the stain was tested in small-scale field test. This report provides an overview of the findings and provides recommendations for future work. The experiments clearly demonstrated that a non-specific microflora can produce brownstain which led to the hypothesis that microorganisms could be involved in hemlock brownstain. Based on our knowledge of the coastal sawmilling industry a strategy of minimizing fungal infection and rapid handling of the tree breakdown into final wood products could probably be the best approach to help reduce the problem. In terms of future work we recommend that work to understand the mechanism of DDAC in mitigation of the browning take precedence in future work on hemlock brownstain.