Phenotypic measures of developmental instability were used to assess the hypothesis that radiation from Chernobyl in Ukraine directly affects the developmental processes of plants. Fluctuating asymmetry and the frequency of phenodeviants in three species of plants, Robinia pseudoacacia, Sorbus aucuparia and Matricaria perforata, were assessed along a transect from the security zone of Chernobyl towards the largely uncontaminated area 225 km SE of Chernobyl. Measures of developmental instability decreased in a similar way for the three species with increasing distance from Chernobyl, the level of developmental instability being three to four times as large near Chernobyl as in the control area. Developmental instability was positively related to the level of radiation by caesium-137 along the transect. In conclusion, radiation from Chernobyl has resulted in a reduced ability of plants to control the stability of their developmental processes.