Explants of Gelidium versicolor, Grateloupia doryphora and Laurencia sp . were cultivated in Provasoli enriched seawater culture medium (PES) adjusted to several osmolalities (0 .5, 0.7, 1 .0 and 1 .5 Os kg -') and solidities (agar concentration = 3, 8 and 15 g L -') . Osmolality was adjusted by dilution of seawater with distilled water (50, 70 and 100% seawater) and by NaCl addition . Explants of Laurencia sp . and Grateloupia doryphora showed bud regeneration and callus formation . Explants of Gelidium versicolor only showed bud regeneration . Osmolalities of 0 .5 and 1 .05 Os kg -' inhibited or drastically reduced bud regeneration and callus formation . The highest callus formation and bud regeneration were observed at 0.7 to 1 .0 Os kg -'. An increase in the agar concentration of the culture medium was positively correlated with callus formation and negatively correlated with bud regeneration . An increase in the percentage of seawater increased the solidity of the culture medium and was positively correlated with callus formation . Glycerol was an effective carbon source for the vegetative propagation of axenic explants of Grateloupia doryphora, promoting growth and bud regeneration . An increase in glycerol concentration in the culture medium increased its osmolality, inhibiting the growth of the explants and their morphogenetic development .