The rate of mycelial growth of the true dry rot fungus <i>S. lacrymans</i> was found to be essentially the same over nutrient (5% malt agar) and through non-nutrient (brick chippings) substrates (<i>c* 1. 5-6 mm/d) as long as there was adequate nutrition and aeration and no toxic or other inhibitory influences. Furthermore, the rate of growth through brick chippings remained fairly constant irrespective of distance of the advancing hyphae from the food base. The longest sustained period of growth was more than 400 days, giving a mycelial length of nearly 2 meters. After severance from the food supply growth continued for 7-10 days (9-21 millimeters) for every 100 millimeters of mycelium. The greatest post-severance growth achieved was 136 millimeters in 44 days from mycelium 655 millimeters long. The implications of these findings for the eradication of outbreaks of dry rot are discussed. -- AATA