Comparative immunodiffusion (ID) analyses of H. injluenzae type e capsular precipitinogens showed that lack of reciprocal precipitation does occur among variants of type e strains. This finding is in accord with results of earlier performed agglutination experiments. By means of ID analyses, two capsular precipitinogens, designated e1 and e3, were revealed in both type e variants. However, in one strain variant, the capsular substance contained e1 and e3 in comparable amounts, while the other variant contained e3 with only a minor contribution of e1. In the first-mentioned variant, the association of e1 to e3 appeared to inhibit precipitation of e3 with E3 precipitins from the other variant, as well as absorption of these precipitins by means of e3. Mild acid hydrolysis changed the antigen preparation of the first variant so that e1 was no longer demonstrable. However, e3, similar to those of the other variant and able to form precipitate with and to absorb E3 from this variant, was demonstrated after the acid treatment.