We compared peanut agglutinin and S100 stains on paraffin embedded material from a variety of sites involved in Langerhans cell histiocytosis (LCH). The two techniques were comparable in terms of ease of performance, time taken and cost. Peanut agglutinin produced dense cell surface and paranuclear staining of the characteristic LCH cells seen in lesions, which was easier to distinguish than the more diffuse cytoplasmic staining produced by the S100 technique. This characteristic staining pattern is more specific than that for the S100 protein which is present in a variety of different cells, including some malignant histiocytes. We recommend that peanut agglutinin be used as a routine diagnostic test for all samples suspected of being LCH.