This lead article in a point/counterpoint exchange argues that negative affectivity (NA) has an important substantive role in the job stress process beyond any possible biasing or nuisance effect. Recent recommendations that NA be routinely controlled in job stress studies because of a biasing effect are noted as inappropriate because NA is a likely cause and effect of job stressors rather than just a bias. The nature of bias versus substantive effects is discussed, and evidence for a causal role of NA is provided. The literature on the bias effect is reviewed, leading to a conclusion that NA has not been a serious problem with most job stressor and job strain variables studied. It is recommended that future NA research focus on its substantive role in the job stress process rather than its bias role. (Copyright 1998, John Wiley.)