Twelve cases of malignant spindle-cell and sarcomatoid tumours of the skin of debatable nature were studied by immunocytochemical methods, using four antisera which might help contribute to resolution of the problems. The initial diagnosis made on structural grounds was confirmed by immunocytochemistry in six of eight cases in which a specific diagnosis had been made (one melanoma, three squamous carcinomas and two atypical fibroxanthomas). One case, initially regarded as AFX was reclassified as a squamous carcinoma, while a further case of possible AFX could not be confirmed by immunocytochemical study. Of the four cases in which structural examination was inconclusive, two were identified as squamous carcinomas and one as a melanoma by virtue of tumour markers. The fourth case was an intriguing actin-rich tumour of uncertain nature. Immunocytochemistry, despite certain limitations, has a valuable role to play in the analysis of the problematic spindle-cell malignant and pseudomalignant tumours of the skin.