Protein solubility in 0.5 % KOH and total and available lysine contents were determined in rapeseed meal and cake heated in the laboratory at 130°C for 0, 10, 20, 40, 80 min, and in 9 meals produced by different oil factories. Protein solubility in the cake decreased due to heating from 89.2 to 44.6, and in the meal from 58.6 to 43.4 %, total lysine content decreased respectively from 6.06 to 5.20 and from 5.85 to 4.96 g/16g N, available lysine from 5.20 to 3.95 and from 4.92 to 3.89 g/16g N. The available lysine content was closely related to protein solubility in the meal heated in the laboratory while no such significant relationship was found in 9 meals processed industrially. The in vivo indices of protein value of meal and cake heated for 0, 20, 40 and 80 min, determined with rats, tended to decrease as the heating time was extended from 20 to 40 min, but only in the meal and cake heated for 80 min and having protein solubility 36.3 and 44.3 %, respectively, were all protein value parameters affected significantly. It is concluded that protein solubility in 0.5 % KOH may be indicative of rapeseed meal overprocessing and cake underprocessing.