To evaluate two methods for decreasing and/or diluting the FDG activity in the urinary system, five rats were intraperitoneally given 1,000 micrograms/g of L-lysine 4 times, starting from 60 minutes before iv injection of FDG, and then at 30-minute intervals for 90 minutes. Five rats were used as controls. In a furosemide study, 12 rats were allocated to three groups. Group 1 received iv injection of FDG alone. Group 2 received saline before iv injection of FDG. Group 3 received furosemide (7 mg/kg) and saline (1/30 of body weight). Neither renal uptake nor urinary excretion of FDG had a statistically significant difference: renal uptake; 0.179 +/- 0.011 (L-lysine) vs. 0.119 +/- 0.003 (control) % kg injected dose/g. The % dose excreted and total urine volume were: 15.0 +/- 2.5 to 15.5 +/- 2.5 with 2.98 ml (L-lysine), 22.9 +/- 1.8 to 24.2 +/- 1.5 with 1.41 ml (control). The furosemide study revealed a statistically significant difference: Group 1; 7.57 +/- 4.73, Group 2; 0.686 +/- 0.638, Group 3; 2.37 +/- 2.33% kg injected dose/g (p < 0.01 for Group 1 vs. Group 2, p < 0.05 for Group 1 vs. Group 3). While pretreatment with L-lysine or furosemide failed to decrease renal activity of FDG, saline injection without furosemide markedly decreased urinary activity.