To determine the time of moulting, rate of shell growth, and correlation between shell growth and moulting 4 series totaling 204 Balanus improvisus were reared from day of settling through 64, 57, 13, and 10 days, respectively. Each barnacle was maintained separately in the laboratory on uni-algal cultures of Nitzschia closterium, Chlamydomonas sp., or mixtures thereof. Barnacles were examined daily for exuviae and measured to determine areal increments. At this time the old culture medium was replaced. The barnacle under investigation exhibited more rapid growth in the medium containing Chlamydomonas alone than in a mixed culture of Nitzschia and Chlamydomonas. Although growth in the laboratory was continuous, it was less than that under natural conditions in the Harbor. Moulting was found to occur on the avg. of every 2-3 days in all series maintained. The first 2 moults may be completed even though food is not present, but if further moulting is to take place food must be available. Moulting occurred more regularly when barnacles were fed Chlamydomonas, a sp. which remained in suspension, than when fed Nitzschia, a sp. which tended to settle. Shell growth was found to be continuous but erratic, and there was no indication that there is any correlation between shell growth and any period in the moulting cycle.