SummaryThis study provides the first description of the range and immunogenicity of proteins excreted and/or secreted by living T. trichiura adult worms following their recovery from the human large intestine. Metabolic labelling ofT. trichiura excretory/secretory (ES) products with [35S]‐methionine revealed a range of proteins with prominent components at 52–54 kDa, 35–45 kDa&17 kDa. In contrast, the major component of unlabelled T. trichiura ES, somatic whole worm and isolated stichosome extracts, and of [35S]‐methionine labelled somatic extracts, was present at approximately 47 kDa. Similarly, the major 43 kDa protein present in unlabelled T. muris ES, somatic worm extract and [35S]‐methionine labelled somatic worm extract, was only weakly detected in labelled T. muris ES. Pulse chase experiments demonstrated that after 20 h, the 43 kDa was a prominent component of T. muris ES. These data suggest that the 43/47 kDa protein of Trichuris adult worms is not a major constituent of newly synthesized ES but is either synthesized at a slower rate than other proteins, or sequestered or stored, most likely in the stichocytes, before release. Immunoprecipitations using a range of sera from T. trichiura‐infec ted individuals demonstrated that many of the ES components are immunogenic. Antibody responses were vigorous in children with intense infections and negligible in parasitologically negative children. There was marked heterogeneity in responses to a 17 kDa antigen, with the age profile of anti‐17 kDa antibody levels reflecting age‐dependent infection intensities at the p