Inheritance of thiocyanate and (+)S-methyl-L-cysteine sulphoxide (SMCO) contents were studied in a diallel cross involving five varieties of forage rape. Although both additive and dominance components were significant for the two characters, the greater mean squares of the additive gene effect indicated its greater importance. Non-allelic gene interaction was detected for thiocyanate only. Narrow sense heritability was relatively high for both characters. The general and specific combining ability effects and heterosis of the individual crosses, identified the potential of the cross 'Nevin' × 'Akela' for production of varieties with low thiocyanate content. Thiocyanate and SMCO contents were positively correlated, and they were not correlated with dry matter yield and its components.