This is a two part study designed to evaluate the safety and efficacy of SB-773812 in the treatment of acute schizophrenia. Subjects with acute schizophrenia will be randomized in an adaptive design study to receive placebo, SB-773812 60mg or olanzapine 15mg for 12 weeks in Part A. An interim analysis will be conducted to assess the efficacy and safety of the SB-773812 60mg dose compared with placebo. Based on these data, up to two further doses of SB-773812 will be added to the randomization for Part B.