Sera of rabbits injected with Conjuvac developed high titres of pollen-specific haemagglutinating antibody. Similarly, sera of guinea pigs treated with Conjuvac developed high titres of pollen-specific IgG1 antibody, as assessed using guinea pig passive cutaneous anaphylaxis (PCA). In both species, the immunogenicity of pollen extract was increased by conjugation to alginate to an extent greater than or equal to that resulting from adsorption to aluminium hydroxide. In contrast, in rats, Conjuvac alone failed to induce pollen-specific IgE antibody, and it suppressed the IgE response induced by pollen extract absorbed to aluminium hydroxide.