The present paper examines the hypothesis thar trait cheerfulness, seriousness, and bad mood form the temperamental basis of the sense of humour. American(N = 263)and German (N = 151) adults filled in the state-trait cheerfulness inventory and a sense of humour scale. Correlations between the two inventories showed that trait cheerfulness accounted for most of the variance-in the sense of humour scales with seriousness and bad mood displaying some incremental validity. The sense of humour subscales and the facets of cheerfulness formed a potent first factor in a joint factor analysis of the subscales of the two inventories. While seriousness and playfulness-recently proposed as being the basis of the sense of humour-were indeed related to the sense of humour scales: they contained additional variance and loaded on the subsequent factors of trait seriousness and bad mood. The results are discussed in the context of the necessity of separating affective and mental factors in the sense of humour. (C) 1998 Elsevier Science Ltd. All rights reserved.