 This will be a placebo-controlled, single-ascending oral-dose study of AMG 581 with a food-effect cohort. Approximately 70 subjects will be enrolled. This study will enroll healthy subjects into 8 cohorts Cohorts 1,2,3,4,5,6,8 and 9, and subjects with schizophrenia or schizoaffective disorder receiving antipsychotic medication into a single cohort Cohort 7. 