The Capillaroscopy Unit of Broussais Hospital has carried out more than 6,000 examinations involving all areas of pathology and more particularly the special role which the method plays in connective tissue diseases. This experience was used to attempt to define the characteristics of the morphological abnormalities of the nailbed capillaries in connective tissue diseases in the adult. The study was deliberately limited to abnormalities of the capillaries themselves, with the exclusion of abnormalities of the pericapillary spaces, abnormalities of blood flow and abnormalities capable of manifesting themselves in the cold; though bearing in mind that the interpretation of a capillaroscopic examination can be perfectly credible only if all such anomalies are taken into consideration. The following capillaroscopic appearances have been included under the heading "morphological abnormalities": dystrophies, dilatations of the loops without megacapillaries, megacapillaries, telangiectasia, filiform loops, regressive capillaries, long loops and microaneurysms. Groups of these morphological abnormalities form more or less typical associations in connective tissue diseases.