In microalgal culture collections, as in many biological resource centres, cryoconservation is the most attractive method for the long-term, secure storage of living material. Nannochloropsis oculata, a marine unicellular alga, is of interest in the field of biotechnology due to its high lipid content. Of various cryoprotectants tested for their toxicity and for their ability to prevent cryoinjury, glycerol ( final concentration 1.1 M) was the most efficient. When glycerol-treated cultures were submitted to a strictly regulated cooling rate (- 3degreesC min(-1)), they attained the control culture density within 13 d after thawing.