The enzyme amylase is produced in large quantities in two mammalian tissues, the pancreas and the parotid salivary gland. A substantial body of biochemical and genetic evidence is consistent with the existence of distinct genes encoding salivary and pancreatic amylases, but testcrosses in mice have indicated that the two putative loci must be very closely linked. We have studied crosses between two pairs of inbred mice that differ with respect to electrophoretic mobility of salivary and pancreatic amylases. Among 343 potentially recombinant chromosomes examined, no recombinants were found. Our data sets an upper limit of 0.87 cM (P = 0.95) for the distance between the salivary and pancreatic loci.