Summary:The response, of cell suspension and callus cultures of celery to asulim (6–600 μmoll−1) in the nutrient medium was compared with that of seedlings. The callus cultures were treated.at three slages of differentiation: undifferentiated callus, differentiated callus on which embryoids had developed to the globular and heart‐shaped stage, and finally plantlets which had secondary leaves and roots. Cell division in the suspension culture was enhanced at low concentrations (6 and 12 μmoll−1) and inhibited at higher concentrations Cell expansion was unaffecte by the presence of asulam In differentiated tissue the growth stimulation at low concentrations was absent. and there was a steady decline in accumulation of fresh weight with increasing concentration. Root length and number of laterals of intact seedlings showed a similar pattern, indicating that the response of the tissue to asulam was not radically altered by diffe