The possibility of cryopreserving B. amphitrite (Cirripedia; thoracica) nauplii is explored. The effects on the postthaw survival of a range of cryobiological variables are reported; three different cryoprotectants (ethylene glycol, EG; dimethyl sulfoxide, Me sub(2)SO; and glycerol, GL), the influence of the final temperature (-20, -30, -40, and -50 degrees C), and the effect of transferring to liquid nitrogen (-196 degrees C) were studied. The larvae showed increasing susceptibility to cryoprotectant concentration. Equilibration of larvae for 15 min at 5 degrees C with each of the cryoprotectants revealed and GL was the least toxic. EG at 3 to 4 M did not cause marked damage as the equilibration period was extended up to 2 h. This was not true with Me sub(2)SO and GL. The postthaw survival rate decreased as the final temperature was reduced, and none of the larvae revived after thawing from -50 degrees C. The postthaw survival with 2 mol/liter EG as the cryoprotectant ranged from 86% after cooling to -20 degrees C to 56% after cooling to -40 degrees C. The larvae that were transferred to liquid nitrogen from different temperatures revealed that the greatest survival (36%) was achieved when the larvae were transferred from -40 to -196 degrees C. When the larvae reared after cooling to -40 degrees C and then transferring to liquid nitrogen, the rate of subsequent metamorphosis was 30% in the case of EG at 3M. Me sub(2)SO and GL gave results that were inferior in comparison to those obtained with EG