Semipermeable membrane devices (SPMDs) are sampling and concentrating devices comprised of a thin polyethylene membrane containing a small quantity of triolein. They have previously been used to sample air, water and sediments and have concentrated fish tainting compounds from pulp mill effluents. The ability to induce mixed function oxygenases (MFOs) is a property of a variety of organic effluents, but the compound(s) responsible for induction have not been identified. We wanted to see if SPMDs would accumulate the MFO-inducing chemical(s) from pulp mill effluents and oil refinery effluents. Dialysates of effluent-exposed SPMDs induced ethoxyresorufin-O-deethylase (EROD) activity in a fish (Poeciliopsis lucida) hepatoma cell line, PLHC-1. In pulp mill effluents and oil sands mining and refining wastewaters, potencies varied greatly, from a few to thousands of pg TCDD-EQ/g SPMD. Low levels of inducers were seen in four pulp mills on the Athabasca R., and higher levels at one New Brunswick bleached sulphite and two Ontario bleached kraft pulp mills. The highest levels of MFO inducers were in SPMDs deployed for 14 days in wastewater from an oil sands upgrading facility, as well as SPMDs deployed at two sites on Athabasca River tributaries in the oil sands area. This suggests that natural erosion and weathering, as well as industrial processing of the oil sands, can release potent MFO inducers. Background (reference) induction by SPMD extracts ranged from non-detectable (<1) to 20 pg TCDD-EQ/g SPMD. Reactive clean-up of one of the bleached kraft mill effluent-exposed SPMD extracts on a sulfuric acid/silica gel column resulted in loss of the inducer(s), which suggested a polyaromatic hydrocarbon-type of inducing chemical(s), rather than a dioxin or furan inducer. SPMD deployments proved useful in the detection of inducers within the pulp mill process streams as extracts of SPMDs exposed to untreated bleached sulphite effluent were ten to twenty times as potent as those from secondary-treated effluent. Little is known about the nature and identity of the MFO inducers from pulp mill and refinery effluents, but the use of SPMDs as concentrators of MFO-inducing substances appears a promising avenue for future research.