Isocyanates are one of the main causes of occupational asthma. The aim of this investigation was to study the possible genetic background of isocyanate-induced asthma under consideration of the atopy status and different lung function parameters. We investigated the human leukocyte antigen (HLA) genes DRB1,3,4,5, DQB1, and DQA1 in 55 isocyanate-exposed patients with workplace-related dyspnea (32 asthmatics, 23 nonasthmatics) and 90 nonexposed controls. In contrast to other studies, we found no significant differences for any HLA class II allele tested in our study group. Furthermore, no significant differences concerning the aspartic amino acid residue 57 of DQB1 was observed. Therefore, we are unable to confirm an involvement of a specific HLA class II allele or DQB1-Asp57 in conferring susceptibility to isocyanate asthma in our study group.