The reporter gene for chloramphenicol acetyltransferase (CAT) was introduced into white spruce (Picea glauca (Moench) Voss.) protoplasts by electroporation. CAT transient gene expression was increased by increasing the concentration of pCaMVCN plasmid and was affected by the level of the applied voltage. Highest CAT activities were obtained after electroporation with a pulse of 350V.cm(-1) having an exponential decay constant of approximately 105ms. Linearized plasmid constructs gave much higher levels of CAT activity than circular plasmid. Attempts to use the Escherichia coli β-glucuronidase gene (β-GUS) as a marker gene revealed very high levels of β-GUS-like activity in electroporated protoplasts. This activity was mainly due to a small molecule and may mask successful transformation since β-GUS-like activity increased when plasmid DNA was present during electroporation.