In the root rot complex in crocus, three different causes have been identified. Under conditions prevailing in The Netherlands, free-living nematodes (Pratylenchus penetrans andP. pratensis) seem to be of minor importance. The present study has shown that roots are incidentally invaded byStromatinia gladioli; the corms and leaf-sheaths appear to be less susceptible to this pathogen. Crocus is often planted in soil known to be contaminated by this fungus. It is not clear why root rot can only occasionally be ascribed to this cause. Further results indicate thatPythium spp. play a major part in the development of root rot.