During cold treatment of Zea mays L. plants there was a decrease in the level of Fv/Fm and in the quantum yield of photosynthetic electron transport. The degree of damage depended on the ambient temperature and on the irradiance (I). The lower the temperature and the higher the 1, the more pronounced damage occurred. This suggests that photoinhibition has an important role in the cold damage to young maize. Although there was no damage in complete darkness even at low temperature, the repair processes needed a normal temperature.