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Inhibins (INHs) are dimeric glycoproteins composed of an alpha (-alpha) subunit and one of two possible beta (beta-) subunits (betaA or betaB). The aims of this study were to determine the frequency and distribution of INH beta (betaA and betaB) subunits in normal, hyperplastic and malignant human endometrium. Endometrial tissue was obtained from normal, hyperplastic (simple, complex and atypical) and endometrioid adenocarcinoma (EC) and INH-alpha, -betaA and -betaB were labelled using immunohistochemistry and immunofluorescence. INH-betaA and -betaB labelling was increased significantly between the proliferative and secretory phase (p<0.05). The lowest labelling was demonstrated in EC, being significantly lower than in secretory phase (p<0.01) and in simple, complex and atypical hyperplastic tissue (p<0.05). For inhibin-betaB, the most intense labelling was noted in atypical hyperplasia compared to EC (p<0.05). A strong colocalisation of inhibin-alpha and -betaA could be demonstrated in malignant endometrial tissue, suggesting the production of inhibin A within the tumour. Additionally, only limited colocalisation of inhibin-betaB with -alpha subunit could be observed, suggesting the synthesis of activin B rather than inhibin B in malignant endometrium. In conclusion, INH-betaA and -betaB were labelled in normal, hyperplastic and malignant endometrium. Hyperplastic tissue labelled more intensely than EC for the presence of INH-betaA and -betaB, suggesting a substantial function in endometrial pathogenesis and an important role in endometrial carcinogenesis.