The Western Neuro Sensory Stimulation Profile (WNSSP) was developed to assess cognitive function in severely impaired head-injured adults (Rancho levels II-V) and to monitor and predict change in slow-to-recover patients. Slow-to-recover patients are those who remain at Rancho levels II and III for extended periods of time and are candidates for sensory stimulation programs. Although sensory stimulation is considered beneficial, its utility has not been documented, partly because of the absence of formal measurement tools. The WNSSP consists of 32 items which assess patients' arousal/attention, expressive communication, and response to auditory, visual, tactile, and olfactory stimulation. It was administered to 57 patients with a mean age of 29 years at a mean time of eight months after injury. Statistical analyses indicate the WNSSP to be a reliable, valid measure of cognitive function. WNSSP means differ at each Rancho level, and ranges of scores at each level are sufficiently broad to demonstrate improvement within as well as across cognitive levels. Subjects who later improved performed significantly better on initial testing than did those who did not improve, suggesting prognostic ability of the WNSSP. Our data support other investigations which emphasize that some slow-to-recover patients experience significant improvement. The WNSSP can be a useful tool for studying the recovery process and evaluating treatment programs for slow-to-recover patients.