Major histocompatibility complex (MHC) genes are classical examples of "good genes" because of their critical participation in fighting and eradicating pathogens. Here, we investigated the inheritance of alleles across a highly polymorphic MHC class II B gene in a socially monogamous raptor, the lesser kestrel Falco naumanni. Allele segregation patterns from parents to offspring were monitored in 44 breeding pairs and 228 nestlings. We found that a particular array of closely related alleles, defined by the presence of two of the three commonest alleles (only three alleles exhibit frequencies larger than 10 % in the studied populations), showed significant transmission ratio distortions when inherited from males (k 0 0.702 ± 0.188, p < 0.001), but not when inherited from females (k 0 0.563 ± 0.207, p 0 0.19). We believe that this result is consistent with the targeting of genetically loaded spermatozoa by female kestrels. Our analyses do not allow discerning, however, whether this pattern is predominantly driven by sperm competition or differential maternal allocation. This trend, nonetheless, would agree with the contrasting relative frequencies of these alleles between Communicated by J. A. Graves Electronic supplementary material The online version of this article