Three studies examined the psychometric characteristics of short Positive Affect (PA) and Negative Affect (NA) scales as a function of varying descriptors, time frames and rating formats. The stability of affective structure across time periods and response modes was also evaluated. Study 1 examined the effect of six specified time periods on mood ratings. Both orthogonal and oblique factor analyses indicated that highly convergent PA and NA dimensions emerged in each solution; moreover, in the oblique solutions the correlation between the factors did not systematically vary across the different time periods. Correlations between brief NA and PA scales were also unaffected by the specified time frame but were consistently influenced by the descriptors comprising the scales. Study 2 investigated the psychometric properties of several short PA and NA scales. Most showed reasonable internal consistency reliability and convergent correlations; however, the discriminant correlations between PA and NA scales varied as a function of their component terms. Study 3 investigated the effects of different response formats. Analyses indicated that highly similar factors emerged regardless of format but that the response mode did affect the discriminant correlations.