Altered human locomotion is a cardinal symptom of several psychiatric disorders. Activity levels are, for example, elevated in illnesses such as mania and ADHD and attenuated in bipolar and seasonal depression. Disrupted sleep is an additional marker in depression and other psychiatric maladies such as post traumatic stress disorder. Circadian rhythm changes are also a significant marker in depressed or psychotic patients, and our Motionlogger Actigraphs have the ability to quantify these changes and monitor both long-term sleep and daytime activity levels of subjects in their natural environment. These innovative devices provide the clinician with a valuable tool to objectively document these parameters as well as the effects of intervention strategies.