Using a combination of immunoprecipitation and polyacrylamide gel electrophoresis techniques, patterns of antibody responses to a number of components in rye pollen extract have been studied in hyperimmune mouse sera. Common laboratory strains of mice were investigated, including AKR, C3H/He, SwR, Ist, Asn, Balb/c, C57BL10, DBA2 and BD1:F1 hybrids. All strains responded vigorously to the immunisation protocol used (rye pollen extract/alum followed by a booster dose in aqueous media) when tested with non-discriminating assay procedures such as haemagglutination or passive cutaneous anaphylaxis directed against the whole rye pollen extract. However, markedly variable antibody responses were observed between strains and between murine and human sera when considered in relation to individual rye extract components. Particularly noteworthy was the relatively poor response of all mice to the low molecular weight rye antigen component (11,000 daltons). This material was readily detected by human sera derived from pollenosis patients. Notable also was the fact that no single rye component was detected by all mice sera. These results illustrate the complex serological response induced by heterogeneous antigen mixtures, such as grass pollen extracts.