I . Evaluation of the germ meal (CGM) of carob seed (Ceratonia siliqua) and its protein isolate was carried out with weanling rats. Comparisons were made with casein, soya-bean meal, whole defatted egg and a soya-bean protein isolate (Promine-D) as protein sources. The growth-promoting effects and certain biological indices were evaluated using the protein efficiency ratio (PER), biological value (BV) and net protein utilization (NPU) bioassay procedures.2. The unsupplemented CGM had a PER of 1-66*0.09 and an NPU of o*58fo.o13. Addition of DLmethionine at 4, 8 and 12 g/kg diet resulted in a PER of 1.95fo.1 I, 2-01 f 0 1 I and 1.9of01 I respectively.The corresponding BV values were 0~80*0.003,078 f 0-015 and 0.74fo.01 I , and those for NPU 0.69 fo.013, 0.66-+0.026 and 0 6 3 fo020 respectively. The addition of amino acids improved the PER (2*24-2-59), BV (0.784.79) and NPU (0.71-0.73) values.3. The BV and NPU assays for the unsupplemented carob germ isolate were low (BV 0.36&0.016, NPU 0~35fO*ol5). Supplementation with amino acids resulted in a positive increase with values of 0.66fo.013 and o Q f o o 1 3 for BV and NPU respectively.The nutritional potential of certain agricultural by-products has not been adequately studied, a fact that limits their utilization as animal food ingredients. The shortage and high prices paid for protein concentrates in livestock feeding has stimulated nutritional and economic feasibility studies of by-products and wastes as sources of protein. It appears therefore that the resources in such products need to be further exploited and thoroughly evaluated nutritionally.Carob germ meal (CGM) is a by-product obtained from the germ of the carob seed (Ceratonia siliqua) after the separation of gums and the fibrous coating of the seed. The milled germ has a uniform consistency and is a light greyish colour. It provides in the dry state as fed, approximately 955 g dry matter and 426 g crude protein (nitrogen x 6.25)/kg. The current annual production of this by-product in Greece is approximately 2000 t and is likely to increase.The literature contains only one report by Ferreira (1964) of the evaluation of CGM protein. The CP content varies from 488 to 507 g/kg and biological indices (biological value (BV) 0.51, protein efficiency ratio (PER) 1-20) have been reported for the rat.In the present study well-established rat bioassay procedures were used to assess protein quality and obtain information on the nutritional value of CGM. An attempt has also been made to prepare a protein isolate from the CGM and evaluate in a comparative study its performance in the rat. The biological indices measured were BV, net protein utilization (NPU), PER and growth response of the rats to different levels of amino acid supplementation. E X P E R I M E N T A L Analytical proceduresStandard methods tor moisture, CP, diethyl ether extract, crude fibre and ash were those described by the Association of Official Analytical Chemists ( I 970). Gross were extracted by boiling 0.5 g CGM in IOO ml distilled w...