Metrology of mineral fibres by electron microscopy was carried out in thoracoscopy specimens ("normal" parietal pleura, pleural plaque, tumour, lung) obtained from different sites in 19 patients: 9 exposed to asbestos and 10 non-exposed controls. With regard to results concerning the parietal pleura, the differences in exposure of the patients (as revealed by history) were not reflected by metrological characteristics (nature and number of fibres, size, topographical distribution) and it was impossible to distinguish the exposed cases from the controls. The number of fibres ("non-measurable presence" being 130.10(3) fibres/g) did not differ significantly between the two "exposed" and "non-exposed" groups. By contrast, the number of fibres found in lung biopsies was in general very high in exposed patients (up to 379.10(3) fibres/g.) In 3 non-exposed patients, there was no asbestos in the lung. Broadly speaking, metrological data were similar to those previously obtained in other cases and using surgical or autopsy specimens. This reinforces the validity of the method of metrology in thoracoscopic specimens and confirms the complexity and difficulties of assessment of pleural involvement. The advantages of study of early pleural specimens obtained under thoracoscopic control in comparison with surgical or autopsy specimens remains to be determined in a larger number of cases. The safety of the method should be emphasized, no complications having been seen in this series.