A simple and rapid technique is described for the separation of different microalgae from mixed cultures. The technique relies upon density gradient centrifugation in the silica sol Percoll, thus separation is achieved on the basis of differences in buoyant density. Upon centrifugation in Percoll density gradients, microalgae form discrete bands at particular positions within the gradient. If the banding positions for different algae are sufficiently different they can be readily separated by fractionation of the gradient. Photosynthetic activity and subsequent growth of microalgae is unaffected by centrifugation in Percoll.