Various strains of algae were tested under conditions of high light intensities at different temperatures. Differences in growth rate were studied and the better strains selected. By prolonged exposures it was tried to further adapt promising strains to such conditions. No increase of the light saturation level of growth could be noticed after seven months exposure to intensities of 0.25 cal/cm2 min. On the other hand, for several strains an exposure during some weeks appeared to suffice for adapting the cells to a given temperature. During the summer of 1953 growth yields of various promising strains were studied in small outdoor culture devices. Average yields of 20 g/m2 day and efficiencies of light energy conversion of 8 % were observed during July and August. Later in the season both yields and efficiencies declined. These figures imply that during the whole growing period the observed yields were considerably (about twofold) higher as those found in our earlier algal culture experiments.