The composition and nutritive value of leaf protein concentrates (LPC) from various cultivars of potato and tobacco, m and various species of lupin, were investigated with special respect to the content and effect of anti-nutritional substances. Biological value (BV) and true digestibility (TD) of proteins were determined in rats using the Thomas-Mitchell balance method. No distinct differences in amino acid composition of proteins extracted from particular plants were found. The nutritive value of concentrates from potato haulm was not correlated either with their amino acid composition or solanine content. LPC from cv. Nysa contained the highest amount of solanine (1015 mg kg −1), but its protein was of the highest biological value (62). Both BV and TD of protein extracted from the leaves of bitter lupin were significantly lower than these from sweet lupin (BV = 50 and 62, TD = 77 and 81, respectively). Nicotine contained in LPC from tobacco had lethal effects on some of the rats. It was concluded that anti-nutritional and toxic substances present in the green matter of plants can penetrate LPCs and in some cases impair their nutritive value. Thus, in vitro tests cannot provide an adequate basis for the prediction of LPC quality.