Seed from Lathyrus sativus L., with a low content of β-N-oxalyl-L-α, β-diamino-propionic acid (ODAP), was evaluated as an ingredient (LM) in swine diets. The first experiment involved 45 pigs fed LM, containing 27% protein (CP) and 3 g ODAP kg−1, as 0, 10, 20, 30 and 40% of starter diets (20% CP) over a 6-wk period. In exp. 2, two types of LM (0.9 and 2.7 g ODAP kg−1) were each included as 0, 10, 20 and 30 of mash diets fed to 84 pigs from 25 to 100 kg liveweight. The effects of pelleting and supplementation with 1 and 2 g methionine kg−1, for LM diets containing < 0.5 g ODAP kg−1, were examined in the final experiment using 80 growing-finishing pigs. Increasing the LM content above 10% of the starter diet reduced average daily gains (ADG) and feed intake (ADFI) but feed conversion (gain/feed; G:F) was unaffected (P > 0.10). In exp. 2, ADG declined as the dietary content of either LM increased. The lower-ODAP LM-fed pigs had relatively higher ADFI (P < 0.01) and ADG (P < 0.05) but slightly lower G:F (P < 0.08). Consumption of lathyrus led to higher (P < 0.01) liver and kidney weights and lower (P < 0.05) protein content in the longissimus dorsi. Pelleting the diet improved ADG (P < 0.01) and G:F (P < 0.05) but did not prevent the LM-effect on growth rates. Increasing the total sulfur amino acid content of the diet from 0.48 to 0.66% had no beneficial effect on live or carcass measurements. Using a method capable of detecting 100 ng ODAP per g fresh tissue, no residues were found in the loin muscle of LM-fed pigs. The results suggest that anti-nutritive constituents (e.g. anti-trypsin and anti-chymotrypsin), rather than ODAP, limit the potential of lathyrus seed as a feedstuff for swine. Key words: Pig, lathyrus, growth, carcass, neurotoxin