It is now well established that the environment plays an essential role in the morphology and evolution of galaxies: in particular, the HI gaseous content is often deficient for galaxies in clusters, and the deficiency increases towards the cluster center (cf for the Virgo cluster: Chamaraux et al 1980, Cayatte et al 1988, in prep). The gas is mostly deficient in the outer parts of galaxies, which considerably reduces the size of HI disks (van Gorkom & Kotanyi 1985). However the central gaseous

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... content, usually under the form of molecular hydrogen traced by CO emission, seems normal, at least in the Virgo cluster, the only one surveyed at millimetric wavelengths (Kenney & Young 1986).