A method for assessing affect states among older people with Alzheimer's disease was developed for use in a study designed to evaluate a special care unit for such residents of a nursing home. The 6-item Philadelphia Geriatric Center Affect Rating Scale was designed for the use of research and other staff in assessing positive affect (pleasure, interest, contentment) and negative affect (sadness, worry/anxiety, and anger) by direct observation of facial expression, body movement, and other cues that do not depend on self-report, among 253 demented and 43 nondemented residents. Each affect scale was highly reliable, expressed in estimated portions of a 10-minute observation period when the affect expression occurred. Validity estimates were affirmative in showing discriminant correlations between the positive states and various independent measures of social and other outwardly engaged behavior and between negative states and other measures of depression, anger, anxiety, and withdrawal. Limited support for the two-factor dimensionality of the affect ratings was obtained, although positive and negative affect were correlated, rather than independent. Some hope is offered that the preference and aversions of Alzheimer patients may be better understood by observations of their emotional behaviors and that such methods may lead to a better ability to judge institutional quality.