Pleiades proper motion dispersion plotted against mass. Data from various studies (including our own) covering from 12 to 0.012 M_⊙ are depicted with different symbols (see the legend within the diagram). Vertical error bars stand for the uncertainties in the motion-dispersion determination, and horizontal error bars account for mass intervals. The dashed line corresponds to the best fit to all data points excluding the least massive datum from Pinfield et al. (1998). The slope of the fit is −0.53, suggesting near-equipartition of energy for stars and brown dwarfs in the cluster. Vertical dotted lines separate the stellar and the brown dwarf domains.