The amount of protein produced per m2 by plants cultivated in soil in a greenhouse at three levels of fertilizer application, for c. 10 weeks, was estimated by Kjeldahl analysis of the TCA-insoluble fraction of freeze-dried material. The quantity of protein extractable for production of leaf protein concentrates was determined by Kjeldahl analysis of non-dried but frozen material after disintegration with a meat mincer and an Ultra-Turrax homogenizer, hydraulic pressing and filtration, and protein precipitation by heat (in two steps) or by TCA. The precipitability was also studied by Folin-Ciocalteu determination of protein. The quality of each protein concentrate was studied by determining nitrogen content (Kjeldahl), digestibility by pepsin and by pepsin+ pancreatin, nutritive value in Tetrahymena tests, and lysine and methionine content (analysed microbiologically).Twenty-nine species and varieties were investigated. Large differences between species were found in all the properties studied. Protein extractability varied between 5 and 80%, while the extractable protein produced per m2 ranged between I and 140 g. The highest digestibility was two to three times greater than the lowest one. In the most digestible species (Amaranthus caudatus), 82% of the N of the chloroplastic protein concentrate was digested by pepsin +pancreatin. The Tetrahymena value generally ranged between 40 and 98, whereas casein gave values of about 75. The lysine content always exceeded the FA0 minimum. The methionine content of most species varied between 2.0 and 2.2% of the hydrolyzed protein.Amaranthus caudatus and the Chenopodiaceae investigated were the most suitable species for large-scale production of leaf protein concentrates for human consumption because they gave high yield of extractable protein and high-quality protein concentrates.