the [*outer*]{} parts (although for the latest-type galaxies we do expect a significant contribution of the dark component in the inner regions as well, Blais-Ouellette et al. 1999). Since the internal velocity dispersions of the compact group galaxy members (250 km s$^{-1}$) are of the same order of their orbital velocities, interactions in the compact-group environment are likely to lead to mergers. In fact, N-body simulations of compact group formation and evolution (Barnes 1989) show that the fate of a compact group is merging in a few crossing times. In order to avoid fast merging, the theoretical expectation is that the compact group environment should change the shapes of the dark matter halos of galaxies that traverse the group, specifically by transforming the single-galaxy halos in a common halo around the group (e.g. Athanassoula, Makino & Bosma, 1997). Our observations cannot test (directly) this hypothesis but do show that the galaxy halos have not been significantly stripped inside R$_{25}$. Nevertheless, mass models using a common halo for the groups added to the individual star distributions of each galaxy should be performed to test this scenario.

The outliers of the Tully-Fisher relation
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It is clear from Fig. 4 that a 