  I discuss the effect of non-radial motions on the small-scale pairwise
peculiar velocity dispersions of galaxies (PVD) in a CDM model. I calculate the
PVD for the SCDM model by means of the refined cosmic virial theorem (CVT)
(Suto & Jing 1997) and taking account of non-radial motions by means of Del
Popolo & Gambera (1998) model. I compare the results of the present model with
the data from Davis & Peebles (1983), the IRAS value at 1 h{-1} Mpc of Fisher
et al. (1993) and Marzke et al. (1995). I show that while the SCDM model
disagrees with the observed values, as pointed out by several authors (Peebles
1976, 1980; Davis & Peebles 1983; Mo et. al 1993; Jing et al. 1998), taking
account of non-radial motions produce smaller values for the PVD. At r <=1
h^{-1} Mpc the result is in agreement with Bartlett & Blanchard (1996)
(hereafter BB96). At the light of this last paper, the result may be also read
as a strong dependence of the CVT prediction on the model chosen to describe
the mass distribution around galaxies, suggesting that the CVT cannot be taken
as a direct evidence of a low density universe. Similarly to what shown in Del
Popolo & Gambera (1999, 2000) (hereafter DG99, DG00), Del Popolo et al. (1999),
the agreement of our model to the observational data is due to a scale
dependent bias induced by the presence of non-radial motions. Since the
assumptions on which CVT is based have been questioned by several authors
(BB96; SJ97), I also calculated the PVD using the redshift distortion in the
redshift-space correlation function, \xi_z(r_p,\pi), and I compared it with the
PVD measured from the Las Campanas Redshift Survey by J98. The result confirms
that non-radial motions influence the PVD making them better agree with
observed data.

Astrophysics