In this study, we examined the viability of measuring personality using computerized lexical analysis of natural speech. Two well-validated models of personality were measured, one involving trait positive affectivity (PA) and negative affectivity (NA) dimensions and the other involving a separate behavioral inhibition motivational system (BIS) and a behavioral activation motivational system (BAS). Individuals with high levels of trait PA and sensitive BAS expressed high levels of positive emotion in their natural speech, whereas individuals with high levels of trait NA and sensitive BIS tended to express high levels of negative emotion. The personality variables accounted for almost a quarter of the variance in emotional expressivity.