AbstractThis paper reports the isolation of a phenotypically stable line of Chinese hamster ovary cells which exhibits a temperature dependent alteration in the transport of some purines. The alteration manifests itself for the uptake of guanine, hypoxanthine, azaguanine and guanosine but not for adenine, adenosine or thymidine. Studies with crude cell extracts suggest that, at the temperature the alteration is being expressed, the HGPRT activity is within the normal range. In cell‐cell hybridization studies the alteration behaves as a recessive genetic trai