Stretches of CAG nucleotides coding for the amino acid glutamine are an important feature of many transcription factors and genes that are involved in neurodegenerative disorders. In an attempt to isolate CAG repeat-containing cDNAs expressed in nervous tissue, we screened a human fetal brain cDNA library with a probe containing a CAG repeat. Five different clones were characterized and found to contain CAG repeats. Sequence data revealed that four of these cDNAs were derived from novel genes. These cDNAs were designated CAG6, CAG12, CAG24, and CAG40 and were found to correspond to transcripts of 5.0, 7.5, 4.4, and 15 kb, respectively. The genes encoding CAG6, CAG12, CAG24, and CAG40 were assigned to chromosomes 12, 16, X, and 12, respectively. For the 5th gene, CAG26/pRHpA, a localization on two different chromosomes was established: 16 and X. None of the repeats showed any length polymorphisms in human DNA.