The presense of C. diphteriae toxin was demonstrated in throat lesions of 47.7 per cent of case with probable diagnosis of diphtheria, by passive hemagglutination test using erithrocytes previously sensitized by diphtheria anti-toxin. From 53.0 per cent of the same patients toxigenous bacilli were isolated. Hemagglutination test was the only positive one in 13.6 per cent of cases and cultivation in 18.9 per cent. The passive hemagglutination tests performed on 42 children, normal or with pharyngitis or tonsillitis but without clinical characteristics of diphtheria were all negative. The procedure described in this paper, of very simple execution can show results in less than two hours and offers great possibility of advantageous application in the diagnosis of diphtheria.
