The anilinopyrimidines constitute a new class of mainly protective, broad-spectrum fungicides with a high activity against Botryotinia fuckeliana, the causal agent of gray mold on a wide range of host plants. The present study was initiated to investigate the genetic basis of resistance to anilinopyrimidines in B. fuckeliana and to assess the frequency of resistant isolates in vineyards in Switzerland exposed to experimental applications of anilinopyrimidines. In mating experiments, two sensitive reference isolates were crossed with three anilinopyrimidine-resistant field isolates. The analysis of 72 sexual progeny from six apothecia demonstrated that resistance to the anilinopyrimidine fungicide cyprodinil segregated in a 1:1 ratio and is therefore monogenic. The same segregation ratio was found for resistance to the dicarboximide fungicide vinclozolin. Resistance to cyprodinil segregated independently from resistance to vinclozolin. From 1993 to 1995, isolates of B. fuckeliana were collected in Switzerland from five vineyards that differed in their anilinopyrimidine spray history. Of a total of 303 isolates tested in vitro, three anilinopyrimidine-resistant isolates were detected in two vineyards where the cumulative number of treatments was between two and nine. The results of the study are discussed with respect to the implementation of an antiresistance strategy in Switzerland.