  (context) Different cosmological data are consistent with an accelerated
expansion produced by an exotic matter-energy component, dubbed "dark-energy''.
A cosmological constant is a possibility since it satisfies most of the
observational constraints. (aims) In this work, the consequences of such a
component in the dynamics of groups of galaxies is investigated, aiming to
detect possible effects in scales of the order of few Mpc. (methods) The
Lema\^itre-Tolman model was modified by the inclusion of the cosmological
constant term and, from the numerical solution of the equations of motion, a
velocity-distance relation was obtained. This relation depends on two
parameters: the central core mass and the Hubble parameter. The non-linear fit
of such a relation to available data permitted to obtain masses for five nearby
groups of galaxies and for the Virgo cluster as well as estimates of the Hubble
constant. (results) The analysis of the present results indicates that the
velocity-distance relation derived from the modified Lema\^itre-Tolman model as
well as that derived from the "canonical'' model give equally acceptable fits
to the existent data. As a consequence, any robust conclusion on the effects of
the cosmological constant in the dynamics of groups could be established. The
mean value of the Hubble parameter derived from the present study of local
flows is H_0 = 65\pm 7 km/s/Mpc.
