The presence of trachoma antibody in eye secretions of Saudi Arab children appears to be a direct response to the infecting organism. In 35 of 36 cases, the trachoma antibody type found in eye secretions was identical to the strain type isolated concurrently. Strain types were identified by use of donkey hyperimmune sera prepared against types 1, 1b, and 2. The specificity of the sera was enhanced by absorption with trachoma antigens of heterologous type. Similarly, antibody types were determined by absorbing samples of eye secretions with types 1, 1b, and 2. Complete absorption of trachoma antibody activity was achieved only by the antigen type homologous to the patient's own strain. In one instance, antibody could not be typed. No change in antibody or strain type was seen in four children examined twice during a 3- to 6-month period. Typing of trachoma antibody from eye secretions has potential as an immunological and epidemiological tool.