Cotton [Gossypium hirsutum] seedlings became more resistant to soreshin disease, which is incited by R. solani, as they aged 5-14 days after planting. The concentration of catechins in hypocotyls of seedlings also was directly related to seedling age. The growth of 3 R. solani isolates was inhibited by (+)-catechin in a basic salts solution containing either sucrose or sodium polypectate (NaPP); inhibition of growth was directly related to catechin concentration. Thus, catechins present in seedling hypocotyls of cotton may contribute to the age-related resistance to soreshin through inhibition of pathogen growth. Polygalacturonase (PGase) activity in the NaPP medium was inhibited by (+)-catechin in cultures of the slightly virulent isolates C70 and W18, but not in cultures of the more virulent isolate 63SD2. When PGase activity of 63SD2 was expressed per unit of fungal growth. PGase activity was directly correlated with catechin concentration of the culture medium. This suggests that catechin may have induced PGase synthesis.