Effects of pressure on cerebrospinal fluid (CSF) formation were studied in dogs with a recirculatory spinal perfusion tracer clearance technique that does not require steady-state conditions. The data permit statistical analysis of the relationship between the rate of CSF formation and pressure for individual animals. Most animals showed no statistical relationship between CSF formation and intracranial pressure (ICP) and/or cerebral perfusion pressure (CPP). In this study, a disturbance of cerebral blood flow (CBF) autoregulation may have been present in five animals on the basis of CPP reductions, and four of this latter group showed formation to decrease with increasing ICP. It is suggested that CSF formation is normally pressure insensitive. With impaired autoregulation of CBF, formation may follow CBF and CPP passively.