Leaf rust is one of the most important airborne pathogens of rye and appears regularly in all winter rye growing areas. Apart from the application of fungicides, breeding for resistance is the most effective method against leaf rust. During the period 2000-2002 altogether 1277 single-pustule-isolates (SPI) were collected to estimate the virulence structure of leaf rust by testing their reactions on a differential set consisting of 23 inbred lines. During the years of investigation, nine of these lines exhibited virulence frequencies over 50%, suggesting low resistance. With frequencies from 1 to 18% 12 lines still showed high resistance. Corresponding virulences could be found for all tested differential lines in Germany. The percentages of high virulent isolates rose from 4 to 15% during three years. A high diversity could be observed in all regions of Germany every year. Experiments regarding shifting of virulence depending on the period showed an increase of virulence frequencies for most differentials and an occurence of high virulent isolates at the end of the period. Genetic analysis led to the identification of four resistance genes. The genes of the lines H54/9 and S4084 could be localized on chromosome 1RS, the genes of the lines H26 and 94107 on chromosome 4R. Due to the high diversity and complexity of the isolates and the presence of corresponding virulences for all tested lines, the use of these race-specific resistances would probably show no durable effect against leaf rust. An alternative could be the use of new effective race-specific resistance and their combination with quantitative resistance which might lead to durable resistant rye cultivars.