There are two versions of human brain glycogen phosphorylase (B-GP) cDNA in the literature that differ significantly in their C-terminal coding and 3' untranslated regions; one isolated from human fetal brain, and the other from human brain astrocytoma cell line U251. A 280 bp absence in the cDNA sequence isolated from human brain astrocytoma cell line U251 changes the predicted protein length from 842 aa (estimated from fetal brain cDNA) to 862 aa. RNA and genomic DNA were isolated from U251 cells and the 280 bp region of interest was amplified by the polymerase chain reaction (PCR). Sequence analysis of the amplified region has unexpectedly confirmed the presence of the 280 bp in U251 RNA and genomic DNA. Thus, the predicted protein length of 842 aa, as reported for fetal brain glycogen phosphorylase, is most likely the correct one.