On the basis of multislit spectroscopy of 180 stars in the ionising cluster of 30 Doradus we present reliable radial velocities for 55 stars .
We calculate a radial velocity dispersion of \mathbf { \sim 35 } km s ^ { -1 } for the cluster and we analyse the possible influence of spectroscopic binaries in this rather large velocity dispersion .
We use numerical simulations to show that the observations are consistent with the hypothesis that all the stars in the cluster are binaries , and the total mass of the cluster is \sim 5 \times 10 ^ { 5 } M _ { \odot } .
A simple test shows only marginal evidence for dynamical mass segregation which if present is most likely not due to dynamical relaxation .