['We recently reported that 95% of chondroblastomas harbour a p.K36M mutation in either H3F3A (chromosome 1) or H3F3B (chromosome 17), with the majority involving H3F3B. The aim of this study was to assess the expression of the K36M-mutated protein by immunohistochemistry in a large group of tumours.', 'One thousand eight hundred and ninety-four tumours, including 85 chondroblastomas and 10 clear-cell chondrosarcomas, were studied; of these, 82 chondroblastomas and one clear-cell chondrosarcoma known to harbour the H3F3 p.K36M mutation expressed the mutated protein. Three chondroblastomas and nine clear-cell chondrosarcomas wild type for H3F3A/H3F3B were negative for p.K36M immunoexpression. The remaining 1799 cases tested, 545 of which were known to be wild type for the H3F3A and H3F3B p.K36M mutations, included 1047 primary bone tumours, and 507 soft tissue and joint tumours. Two hundred and forty-five other tumour types not expected to harbour the mutation were negative for p.K36M immunoexpression.'] Is the H3F3 K36M mutant antibody a sensitive and specific marker for the diagnosis of chondroblastoma?