Three strains of Ophiostoma piceae (Münch) H. & P. Syd. and a mixed bacterial culture were studied for their potential to produce in vitro brownstain in sap of amabilis fir, western hemlock and lodgepole pine and in western hemlock wood. Several microorganisms increased the pH of all sap samples evaluated and a distinct brown discolouration developed in sap of western hemlock and amabilis fir over 3 weeks. Although pH shift influenced brown discolourations of sap, nutrient status and the extractive composition of the sap appeared to be critical for promoting browning of sap. O. piceae strains also produced brown discolourations in sapwood of western hemlock but the mixed bacterial culture caused minor brown staining only. While we have demonstrated a link between microorganisms and brownstain in liquid culture more research is needed to understand susceptibility of amabilis fir and western hemlock lumber to brown discolourations.