The purpose of this study was to evaluate the toxicological effects of 4-hydroxy-2-nonenal (HNE) and malondialdehyde (MDA) on in vitro plant cells using the model morphogenetic system of Daucus carota L. for the production of somatic embryos. It was found that both HNE and MDA inhibited proliferative growth and embryogenesis in D. carota cultures. However, embryogenic capacity was restored when callus cultures were transferred to embryo induction medium without HNE or MDA and the recovery of morphogenetic competence was more pronounced in cultures which had been exposed to MDA as compared to those which had been treated with HNE. Also, differential responses between embryogenic and nonembryogenic cultures were observed in relation to the delivery of aldehydes in different culture media. This paper reports, for the first time, the toxicological effects of HNE and MDA on in vitro plant cells. The significance of these findings in relation to the control of in vitro development in plant tissue cultures which are used in biotechnology programmes is discussed.