Hypertonic saline (HTS) infusion in "uncontrolled" hemorrhagic shock (UCHS) leads to increased bleeding from injured vessels, fall in mean arterial pressure (MAP), and early mortality. The effect of injured vessel size on blood loss in response to HTS treatment was studied in Neurolidal Ketalar anesthetized Hebrew University strain rats. The animals were randomly assorted into 4 groups: In group I (n = 8) UCHS was induced by resection of 8% of the terminal portion of the rats' tail and the animals were untreated. In group II (n = 8) UCHS was induced as in group I and the animals were treated with 5 ml/kg NaCl 7.5% (HTS). In group III (n = 9) UCHS was induced by 50% resection of the animal's tail, and the animals were untreated. In group IV (n = 12) UCHS was induced as in group III and the animals were treated with 5 ml/kg HTS Resection of 8% of the animal's tail was followed by bleeding of 2.6 +/- 0.3 ml and fall in MAP from 107 +/- 7 to 80 +/- 10 torr (P less than .005) within 5 min. Resection of 50% of the animal's tail was followed by bleeding of 4.3 +/- 0.4 ml (P less than .01) and fall in MAP to 41 +/- 6 torr (P less than .001) after 5 min. Infusion of HTS in group II was followed by further blood loss of 4.9 +/- 07 ml within 4 hr while in untreated group I, blood loss was only 3.4 +/- 0.4 ml (P less than .05), MAP remained unchanged, and there was no mortality.(ABSTRACT TRUNCATED AT 250 WORDS)