A Coulter counter and pulse height analyser has been used to study the aggregation of Chinese hamster cells in the presence of concanavalin A (ConA). After incubation of cell suspensions with ConA under standard conditions of agitation equilibrium aggregate size distribution curves are obtained which show that there is a greater proportion of larger aggregates formed than during aggregation in the absence of the lectin. At equilibrium there is a significant population of single cells. The mean number of cells per aggregate increases with temperature and goes through a maximum as a function of ConA concentration. The kinetics of the aggregation process exhibit features consistent with a bridging mechanism of aggregation mediated by the lectin and leading to an enhanced cellular adhesiveness but his process is superimposed on aggregation arising as a result of the inherent adhesiveness of the cells.