The influence of the plant growth regulators 2,4-D, GA3, BA and kinetin, and the polyamines putrescine, spermidine and spermine were tested on axenic in vitro cultures of carposporelings of Grateloupia doryphora. The auxin 2,4D (10-3 M) and the polyamine spermine (10-6 M and 10-3 M) induced a callus (disorganised cell mass that arose from the organised tissue of the carposporeling, as demonstrated by microscopic monitoring of the tissue). Putrescine and spermidine (10-3 M) transformed the carposporelings into cell masses that produced shoots. BA (10-3 M) and kinetin (10-6 M and 10-3 M) were inhibitory. In 10-1 M glycerol-containing culture medium, which is known to induce the formation of morphogenic cell masses, the addition of GA3 M) resulted in the inhibition of the morphogenesis (i.e. shoot emission) in the cell mass. The kinetin at 10-6 M inhibited morphogenesis, whilst at 10-3 M inhibited even the formation of the cell masses. The combination of glycerol (10-1 M) and the auxin 2,4-D (10-6 and 10-3 M) or the polyamines putrescine, spermidine and spermine (10-6 and 10-3 M) resulted in a bigger size of the cell masses that led to a higher amount of shoots per cell mass than in glycerol alone.