The nitrogen utilization pattern of two spe? cies of Leucostoma was examined using virulent isolates of L. persoonii and L. cincta, and two virus-infected hypovirulent isolates of L. persoonii. Virulent L. per? soonii were able to utilize all of 47 nitrogen sources tested except anthranilic acid, cysteine, homocysteine, hydroxylamine, indole, lysine, urocanic acid, methyl- ated purines and pyrimidines. Leucostoma cincta isolates were unable to use these latter compounds, acetamide and the branched side chain aliphatic amino acids: isoleucine, leucine, and valine. The ability to utilize branched aliphatic amino acids might be a species- specific characteristic. A virulent isolate of L. cincta, ATCC62910, also could not utilize nitrate and nitrite. The two hypovirulent L. persoonii isolates had a further restricted list of usable nitrogen sources. In addition to the nitrogen sources above, they were unable to grow on nitrate, nitrite and the branched aliphatic amino acids, as sole nitrogen sources. Growth of the two hypovirulent isolates on glutamic acid and aspartic acid, as well as aromatic amino acids was poor com? pared to virulent isolates. The patterns of inorganic nitrogen utilization were determined in reference to the known gene loci that control the process in fungi. Inability to utilize specific nitrogen sources is likely the result of mycovirus infection. Poor growth on sev? eral utilizable nitrogen sources might be influential in hypovirulence. trees, dieback of young branch tips greatly reduces vigor, and large perennial cankers in older trees often lead to death (Hildebrand, 1947; Rozsanyay, 1977). As fungicides have proven to be ineffective in con? trolling this disease (Biggs, 1989; Chandler, 1974; Hel- ton and Rohrbach, 1967; Royse and Reis, 1978), a biological control agent that could reduce the impact of this disease has been sought. A diseased isolate of L. persoonii (NC14.4A) has been isolated from peach in North Carolina. Isolate NC14.4A is a hypovirulent nonsporulating isolate that contains many virus like particles (VLPs) in its cytoplasm when viewed in the electron microscope (Snyder et al., 1989). The strain contains at least six segments of dsRNA. Isolate HT is derived from isolate NC14.4A by successive hyphal tipping and has lost the viral particle and four of the six bands of dsRNA. HT has wild-type growth rates and can sporulate, but retains hypovirulence (Ham-