Erwin Chargaff studied the nitrogenous bases of DNA. He found that no matter which DNA molecule he analyzed, it always contained equal amounts of adenine and thymine bases and equal amounts of cytosine and guanine bases. Additionally, the width of an A–T pair is the same as the width of a C–G pair. These data suggest that in a double-stranded DNA molecule, adenine must pair with thymine and cytosine must pair with guanine. This pairing is consistent with a uniform base-pair width down the length of the DNA molecule, as Franklin’s data suggested.