We examined the effectiveness of a new laboratory tool – the leukocyte adhesiveness/aggregation test – in the diagnosis of acute appendicitis. A total of 63 patients, mean age 32 (range 10-85) years, admitted for right lower quadrant abdominal pain were assessed clinically, and laboratory tests were performed. Forty-one of the 63 patients were operated on. Ten (15.8%) were found intra-operatively to have a normal appendix, and the remainder had appendicitis. White blood count, number of neutrophils and monocytes, and leukocyte adhesiveness/aggregation were statistically significant in the 28 patients with frank appendicitis. The aim of this paper is the presentation of the leukocyte adhesiveness/aggregation test as an important tool for more precise diagnosis of acute appendicitis.