Antibodies to Propionibacterium acnes(Corynebacterium parvum) serotype I and serotype II in normal human sera were measured using a microtitre bacterial agglutination test. Of 168 sera tested, 53 sera(31.0%) exhibited higher agglutinin titres to serotype I than to serotype II and 34 sera(20.2%) gave higher titers to serotype II than to serotype I. Eighty-one sera(48.3%), however, showed similar antibody titres to both types. Antibodies to serotype I(x) and serotype II(y) showed high correlation(r=0.73, p<0.01) and regression equation was Y=1,078+0.73X. The mean antibody titre($log_2$) of 529 normal sera(male 447 and female 82) to serotype I was $5.49{pm}1.36$, but there was no significant difference between male($5.45{pm}1.36$) and female($5.74{pm}1.36$). Bacterial agglutinin to Propionibacterium acnes in normal sera belonged to a 2-mercaptoethanol resistant IgG class.