Multiple sclerosis (MS) is an inflammatory, demyelinating disease of the central nervous system in which large numbers of T cells enter the brain and cerebrospinal fluid (CSF). To determine whether these cells represent restricted populations, we studied expression of T‐cell receptor Vβ chains on paired samples from the central nervous system and blood of patients with MS or other neurological diseases (OND) using a quantitative polymerase chain reaction. The distribution of Vβ chain expression in blood was skewed, with a significant preponderance of message from Vβ genes 1 through 8 (p = 0.0001). Such skewing was not present in samples from the CSF and brain. Patterns of Vβ gene expression were different among paired samples from spinal fluid and blood and were relatively heterogeneous. Blood and CSF samples from a patient with acute meningitis were studied on two separate occasions. The patterns of Vβ expression changed over 72 hours in both the blood and the CSF. With one exception, no oligoclonal populations of T cells were observed nor were there disease‐specific patterns of Vβ gene expression in the blood or CSF. Samples from 2 MS brains and 1 OND brain expressed patterns of Vβ genes that were different and less heterogeneous than those in paired blood. In addition, expression of Vβ 12 was remarkably increased in the 2 MS brains, suggesting a selective recruitment or expansion of T cells expressing this gene. These data demonstrate that populations of T cells from blood, spinal fluid, and brain differ from one another and can fluctuate during periods of acute inflammation. In addition, studies of brain T cells may be more informative in terms of defining oligoclonal populations of potentially pathogenic T cells than will studies of nonselected CSF T cells.