Standard curve in the soya protein ELISA using a 50% dilution of normal human serum as diluent. Soya protein was diluted 3-fold from 600 ng/ml down to 0.8 ng/ml. In this particular experiment, the O.D. of 0.8 ng/ml was 0.041 (S.D. = 0.001) and that of the blank was 0.025 (0.004). The O.D. of blank, where normal buffer was used, was 0.013 (0.002) (n = 24).