Resin acids and guaiacols are common constituents in pulp mill effluent and are considered to contribute the greatest effect to the acute toxic actions of mill discharge to fish. The objectives of this study were to examine the sublethal toxicity of 14-monochlorodehydroabietic acid (MCDHAA), 12,14-dichlorodehydroabietic acid (DCDHAA) and 3,4,5,6-tetrachloroguaiacol (TeCG) to rainbow trout, Oncorhynchus mykiss. A biological indicator approach was used involving a suite of indicators which spanned several levels of biological complexity, as well as having ecological relevance. These included biochemical responses and effects on swimming performance and disease resistance. The experimentally determined 96-h LC50 values for juvenile rainbow trout were 0.37, 1.1 and 0.9 mg L−1 for TeCG, MCDHAA and DCDHAA, respectively. Using these values as a guideline, sublethal exposure to each chemical for 24 h resulted in a classical stress response and included significant primary (secretion of corticosteroids), secondary (hyperlacticemia, hyperglycemia) and tertiary (reduced swimming performance and lowered disease resistance) effects. Chronic exposure of fish to TeCG for 25 d resulted in most parameters being at control levels with the exception of leucocrit which was elevated, cortisol which was depressed, and disease resistance which remained impaired. This study indicates that the selected parameters may be useful indicators of acute exposure to pulp mill effluent; however, under chronic exposure conditions only disease resistance was a reliable indicator of persistent toxicant exposure.