The influence of food concentration (Chaetoceros calcitrans at 1 x 10 sup(5) and 2 x 10 sup(5) cells ml sup(-1)) and temperature (20 degrees C and 30 degrees C) on the nucleic acid content of the nauplii and the cyprids of Balanus amphitrite, an acorn barnacle, was evaluated. Food concentration and temperature jointly determined the naupliar instar duration. The total naupliar development period lasted 9-11 days at 20 degrees C and was longer when compared to 5-6 days observed at 30 degrees C. Increase in rearing temperature and food concentration positively influenced the size of the larvae. Food concentration influenced the DNA of 3 and 4 naupliar instars and temperature influenced the DNA of 4 and 5 instar nauplii. The RNA content of 4-6 naupliar instars was also influenced by the rearing temperature. Naupliar experience determined cyprid metamorphosis capability. The RNA content of larvae, that had longer total naupliar duration at 20 degrees C, was considerably less than those raised at 30 degrees C. This difference in RNA content was reflected in the capability of the cyprids to successfully metamorphose over 2-4 days, whereas, those at 30 degrees C could do so over 8-16 days. Such differences in the capability to metamorphose will be of critical importance to recruitment and early post-settlement mortality.