William James observed that, within the stream of thought, the ways we think fluctuate as a function of our emotional and physical conditions. Extrapolating from James, we propose that individuals vary along a dimension called levels of thinking. High-level thinking involves thoughts that are self-reflective, demonstrate awareness of emotion, and incorporate a broad perspective. Low-level thinking lacks these properties. Using a stream-of-consciousness methodology, two experiments examined the parameters of level of thinking. Level of thinking is reliably rated, stable over a 2-month interval, and consistent across modality (across writing vs. talking into a microphone). Whereas levels of thinking are positively correlated with measures of negative affectivity, extremes in thinking are linked to indicants of health problems. The second experiment demonstrated that when individuals face uncontrollable noise bursts, they move to lower levels of thinking that preclude awareness of negative emotions. The adaptiveness of thinking on different levels is discussed in terms of James's contributions to our current understanding of health and coping.