The sensitivity of oomycota, saprophytic and pathogenic fungi to urea, ammonium nitrate and UAN (urea plus ammonium nitrate in equimolar solution) was studied in laboratory trials. The compounds were applied in agar in concentrations of 0.06, 0.19 and 0.6M. The most toxic was urea. Ammonium nitrate inhibited the growth of fungi only in higher concentrations. In contrast, the growth of Gaeumannomyces graminis was stimulated by even the highest concentration of 0.6M ammonium nitrate. The fungi most sensitive to urea and UAN were Alternaria tenuissima, Botrytis cinerea, Cladosporium cladosporioides and Pseudocercosporella herpotrichoides. No synergistic effect between the two compounds in UAN was found. Urea was toxic also to Colletotrichum acutatum which does not produce urease. Likewise, the urease inhibitor NBPT did not decrease the toxicity of urea to fungi.