Using 180 F2 progeny of a C57BL6/J × CAST/Eitub/+ F1 intersubspecific intercross, a map of 28 molecular markers (including eight genes) on chromosome 7 surrounding thetublocus was generated. Using 33 obese F2 progeny,tubwas localized approximately 50–52 cM distal to the centromere on mouse chromosome 7 in the interval defined proximally by hemoglobin beta (Hbb), D7Mit38, D7Mit217, D7Mit37, D7Mit96, and D7Mit33 and distally by D7Mit98. Using 39 obese F2 progeny from a similar intersubspecific intercross, a telomeric boundary of the interval definingtubwas defined by D7Mit53; the order centromere–Hbb/tub–D7Mit53/D7Mit328/D7Mit220–parathyroid hormone (Pth)–calcitonin (Calc)–zona pellucida 2 (2p2) was established. By combining the data from the two crosses, the most likely gene order on mouse chromosome 7 is centromere–Hbb–tub–Pth–Calc, thus making it likely that the human homolog oftubresides on 11p15, where the gene order HBB–PTH–CALC is conserved. Assignment of the humantubbyhomolog to 11p15 allows selection and development of polymorphic molecular markers that can be used to examine segregation of a human homolog oftubbyin pedigrees segregating for obesity. The gene sulfonylurea receptor was eliminated as a candidate gene fortubbyon the basis of its map position, approximately 3.1 ± 3.1 cM centromeric of tyrosinase and approximately 14.9 ± 4.8 cM centromeric of Hbb.