[en] Male Sprague-Dawley rats (125-150g) were implanted (im.) with the Walker 256 carcinosarcoma. After both 7 and 10 days, plasma levels of glucagon in tumor-bearing rats were approximately half the level seen in control rats (P < 0.01) even though fasting plasma glucose levels were slightly (but not significantly) less in the tumor-bearing rats. To determine if the tumor degrades the hormone, tumor cells were incubated at room temperature with ¹²⁵I-glucagon (0.075 μCi, 2200 Ci/mmol) in 20mM TRIS-HCl buffer (pH 7.4) with 2.5% bovine serum albumin (total volume of 750 μl) for 45 min. After incubation with tumor cells, only about 25% of the total radiolabel was TCA-precipitable vs 97% in the control (minus tumor cells) incubations. It also appears that the tumor cells may release a substance which degrades hormone. If tumor cells are preincubated for 60 min at 37⁰ then removed from the medium, the incubation medium contains a factor which degrades subsequently added ¹²⁵I-glucagon (57% TCA-precipitable vs 98% in control incubations). That this factor is a protease is suggested by the results of another experiment in which aprotinin (a protease inhibitor, 1 mg/ml), when added along with the labeled glucagon, virtually eliminated degradation by a factor released from the tumor cells (79% TCA-precipitable in the absence of aprotinin vs 94% in its presence and 98% in controls)