The levels of prostaglandin (PG) E2 and 6-keto-PGF1 alpha (stable metabolite of prostacyclin) in plasma and gastric juice were determined in 113 critically ill children and adolescent, and compared to those registered in a plasma control group of 24 children and a gastric juice control group of 15. The gastric juice concentration of PGE2 is our patients [9.2 +/- 3.1 (SEM) pg/ml] was significantly lower (p = 0.001) than in the control group [81.1 +/- 18.1 (SEM) pg/ml]. There were no differences in plasma levels of PGE2 and plasma gastric juice levels of 6-keto-PGF1 alpha between the patients and the control groups. Children who died had lower plasma levels of PGE2 [6.2 +/- 2.2 (SEM) pg/ml] and gastric juice levels of PGE2 [2.3 +/- 0.8 (SEM) pg/ml] than the survivors (p less than 0.05). The gastric juice concentration of PGE2 was also lower in children who suffered important upper gastrointestinal bleeding, although the difference did not reach statistical significance.