A cultural practice which is becoming more common in Dutch tulip-bulb production is peeling of the bulbs by machine. If this method is not used properly old roots can be left on the base of the bulb. An experiment was conducted to investigate if this might be hazardous with respect to development of root rot, caused by Pythium spp., during tulip-flower forcing in the greenhouse. Severe root rot developed in case old roots from bulbs collected from the field were not removed properly. No clear difference was observed between root rot severity of bulbs harvested from patches with above-ground Pythium symptoms and bulbs from a part of the field without above-ground symptoms. Removal of the old roots reduced root rot severity. Treatment of the poorly peeled bulbs with formaldehyde could not prevent root rot completely. Combination of proper peeling of the bulbs and formaldehyde dip gave a crop with a healthy root system.