MeCH=CHCOOH was applied (concns. 0.25, 0.5 and 1.0 mM) on 2 varieties of maize seedlings (SMH 220 and Lober) to study their growth, content of photosynthetic pigments and nitrate reductase (NR) activity. Growth of the seedlings was inhibited and 20-60% decrease of NR activity both in leaves and roots was obsd. A increase in content of photosynthetic pigments in leaves of Lober and chlorophyll in leaves of SMH 220 was evidenced. The SMH 220 variety was more sensitive to crotonic acid than the Lober variety.