Crystals of concanavalin A were obtained in four different morphologies, depending on protein and precipitant (NaNO 3 ) concentration, temperature and pH. The morphologies were round, round rhombic tetrahedron, smooth faceted and well faceted. The growth rate and the rate limiting step of the rounded concanavalin A crystals were investigated. The growth rate as a function of the supersaturation is compared with models obtained from studies of small molecule crystals. The most probable growth mechanism for these round crystals is found to be the rough surface growth mechanism. This was confirmed with electron microscopy. The time when crystal growth ceases was determined and found to be independent of the precipitant concentration.