125I-Leu15-G17-NH2 and 125I-Leu15-G(2–17)-Gly binding. Percent of maximal specific binding of 125I-Leu15-G17-NH2 (A) and 125I-Leu15-G(2–17)-Gly (B) on the five human colon cancer cell lines compared to AR4-2J (rat pancreatic acinar) cells. Specific binding of 125I-Leu15-G(2–17)-Gly to AR4-2J cells was 65 ± 8% and to LoVo and HT 29 cells 57 ± 8% and 51 ± 5%, respectively. Specific binding of 125I-Leu15-G(2–17)-Gly to HCT 116, Colo 320 DM, and T84 cells was not significant. Mean ± SD of seven different experiments, each performed in duplicate.