The effects of surgical trauma resulting from laparoscopic cholecystectomy and open cholecystectomy, were compared by assessing the postoperative acute phase alterations of selected plasma proteins, hormones and lymphocyte subpopulations in fifty-seven patients prior to elective cholecystectomy. Patients were prospectively randomized to undergo either laparoscopic cholecystectomy (n = 30) or open cholecystectomy (n = 27). Duration of operation and general anesthesia was similar in the two patient groups. The laparoscopic cholecystectomy patients had a shorter postoperative stay in hospital (3.1 (0.5) days vs. 7.1 (1.6) days; p < 0.001). In open cholecystectomy patients a significantly greater postoperative acute phase increase in plasma C-reactive protein (p < 0.001), cortisol (p < 0.05), and prolactin blood level (p < 0.001) was recorded. The postoperative acute phase decrease in the blood total-T-lymphocyte count (CD3 cells) and in the activated-lymphocyte count (OKDR cells) was significantly greater after open cholecystectomy (p < 0.05). These results, showing that acute phase responses are less marked after laparoscopic cholecystectomy than after open cholecystectomy, support the concept that the laparoscopic procedure is less traumatic.