The invention provides methods for treating neuropsychiatric disorders such as schizophrenia, Alzheimer's Disease, autism, depression, benign forgetfulness, childhood learning disorders, closed head injury, and attention deficit disorder. The methods entail administering to a patient diagnosed as having a neuropsychiatric disorder a pharmaceutical composition containing (i) a therapeutically effective amount of D-alanine (or a modified form thereof), provided that the composition is substantially free of D-cycloserine, and/or (ii) D-serine (or a modified form thereof), and/or (iii) 105 to 500 mg of D-cycloserine (or a modified form thereof), and/or (iv) N-methylglycine (or a modified form thereof).