We describe a study that examined the distinctiveness of momentary positive and negative affect (PA and NA) and their relationships with blood pressure and heart rate at work in a sample of 67 full-time employees who provided psychological and physiological measurements multiple times a day, over 10 working days. These employees recorded their subjective ratings on personal digital assistant devices programmed specifically for this study, and assessed their blood pressure and heart rate using automatic recording devices, at each measurement period. Results support the distinctiveness of PA and NA. First, within-individual factor analyses confirmed the existence of two underlying factors in the momentary affect ratings. Second, the within-individual correlations between PA and NA scores (-.14), and among the two latent constructs (-.13) were both low in magnitude. Finally, as predicted by theory, NA was significantly related to blood pressure within individuals, whereas PA and blood pressure were unrelated (both PA and NA were related to heart rate within individuals, as predicted).