Experiments were designed to assess-the influence of a number of environmental factors on the growth and survival of laboratory reared juvenile lobsters cultured in individual containers, and to determine some of the factors affecting the locomotor and feeding activity. The effect of temperature and salinity was studied in a factorial experiment and the optimum combination 'for growth estimated by response surface analysis at 20.8oC and 29.8 p.p.t. Temperature and salinity levels in subsequent experiments were maintained at or around the optimum, combination. Container size exerted an influence over the growth rate and significant reductions occurred when the floor area was less than (1-2 x total length of lobster)2. Darkness and low intensity constant illumination were the most favourable lighting conditions but shelter provision enhanced the growth rate under a light-dark regime. Food utilisation was improved by periodic starvation, and although feeding every three days was not sufficient to sustain a high growth rate, daily feeding conferred no advanatage over feeding every two days. Temperature, salinity and ration level exerted the most direct effect on the frequency of moulting, while the other factors had a greater influence on the size -of the moult increment. The locomotor and feeding activity was studied under a variety of light regimes and the effect of shelter, moult stage and food availability recorded. A weak endogenous nocturnal pattern of locomotor activity was found under constant conditions but under other light regimes activity was irregular and little affected by shelter availability. Daily fed animals displayed a more pronounced nocturnal activity pattern associated with feeding activity which was generally confined to darkness with an overt rhythmic component. The daily pattern of both locomotor and feeding activity varied through the moult cycle and considerable variation in response at the individual level emphasized the flexible nature of activity in the juvenile.