Activity of the paraspinals, abdominals, and hip extensor muscles, heart rate, and skin conductance were measured in 13 chronic low back pain patients (CLBP) and 13 controls during static postures and psychological stress. After 10 min of baseline-rest, a subject was tested during standing, 45 degrees bend, maximum bend, posterior and anterior pelvic tilts, sitting, and supine with knees up, followed by mental arithmetic and the cold pressor. The postures were grouped into supported, balanced, and unbalanced categories. Multivariate analyses of variance revealed differences due to posture categories, but not due to group membership. It was concluded that while work is needed to understand normal muscle function during common movements, there is no compelling evidence that back muscle functioning in CLBP patients differs significantly from control subjects.