A series of 38 primary laryngeal and hypopharyngeal tumours, 15 lymph-node metastases and normal tissue were evaluated in frozen sections for the expression of MHC class I and II antigens, using monomorphic monoclonal antibodies (MAbs) to HLA-ABC, beta 2-microglobulin, DR, DP, DQ, HLA-B and polymorphic HLA-ABC antigens. Normal distant mucosa of larynx reacted to anti-class I antibodies but not to anti-class II. In 9 primary tumours (23.7%) HLA class I antigens were not observed. The remaining 29 showed a strong reaction to not observed. The remaining 29 showed a strong reaction to anti-HLA-ABC (heavy chain) and anti-beta 2-microglobulin, although in 3 cases out of 29 no staining was observed with anti-HLA-B locus-specific MAbs. These selective losses were confirmed using the corresponding anti-HLA polymorphic MAbs. For HLA class II molecules, only DR was observed in 3 of 38 cases. Defective HLA class I expression statistically correlates with high scores according to Jakobsson's criteria for histopathological tumour grading. Loss of HLA-ABC antigens was most frequent among the cases with poor differentiation (6/8 cases). On the contrary, class II antigen expression was correlated with a well differentiated pattern and a more favourable prognosis (p less than 0.001). We have found differences in HLA class I expression when comparing primary tumours and autologous metastases (3/9 cases). Immunoprecipitation and SDS-PAGE of class I antigens, Northern and Southern blot analyses of MHC class I genes were performed. We have not detected class I gene rearrangement using HLA coding and locus-specific non-coding probes. However, we have found a class I transcription defect that corresponds with a class-I-negative phenotype.