Solvent-extracted rapeseed meal of B. campestris L. origin, free of active myrosinase and retaining most of its original complement of thioglucosides, was fed to pigs in growing and finishing rations at levels up to 10% of the diet. Cross-treatments of zero and 0.022% iodinated casein were used over the 23- to 45- kg. weight range. Twenty-four gilts and 24 barrows of Yorkshire breeding were involved, and growth rates, digestibility, feed utilization and carcass merit were assessed. The use of either 5 or 10% rapeseed meal significantly depressed rate of gain and feed intake in the growing period (23 to 45 kg.). Iodinated casein had no effect on the response to rapeseed meal. A level of 5% rapeseed meal in the finisher ration had no effect on swine performance. Failure of iodinated casein to counteract the adverse effects of rapeseed meal and the lack of effects of rapeseed meal on efficiency of feed utilization or digestibility of energy and protein indicate that this type of meal differs appreciably from meals previously tested with swine, in terms of physiological effects on the animal. Rate of gain closely reflected feed intake levels; hence, palatability may have been involved. The addition of a myrosinase source (ground rapeseed screenings) resulted in three times as much depression in rate of gain in pigs fed grower rations containing rapeseed meal as occurred in the absence of rapeseed screenings. Reduced gains also occurred with rations containing 5% rapeseed meal fed with myrosinase in the finishing period, and there was evidence of depression in digestibility coefficients for energy and protein due to ingestion of the enzyme source. These results confirm previous findings in vitro and with mice, in which myrosinase was implicated in the toxicity complex of rapeseed meal.