Aflatoxin B1 and sterigmatocystine hemiacetal derivatives were synthesized, and their conjugation to albumins and gelatin and also spectral and immunochemthe specificity and analytical properties of the antibodies produced by immunization with conjugated antigens. The possible mechanism of hemiacetal interaction with proteins is discussed. Based on immune reagents to sterigmatocystine hemiacetal, a test system was developed for determination of sterigmatocystine at the sensitivity of 0.1 ng/ml.