Real-time ultrasonography (US), computed tomography (CT), and biochemical tests were prospectively performed to detect gallstones in 88 consecutive patients immediately after the onset of an attack of acute pancreatitis. The sensitivity of biochemical tests was 84.6% when the patients had three or more positives of five parameters [including serum bilirubin, alkaline phosphatase (AP), gamma-glutamyl transpeptidase (GGT), alanine transaminase (ALT), and alanine transaminase-aspartate transaminase (ALT-AST) ratio]. The sensitivity, specificity, and accuracy were 71.8, 98.0, and 86.4% for US, and 52.9%, 100%, and 79.5% for CT. The sensitivity, specificity, and accuracy were improved to 82.1, 100, and 93.2% by the combination of US and CT, and 94.9, 100, and 97.7% by the combination of US and biochemical tests. Adding CT to the combination of US and biochemical tests resulted in only a slight improvement in sensitivity and accuracy. In conclusion, a combination of US and biochemical tests can provide the best noninvasive method in rapidly detecting gallstones as an etiological factor in acute pancreatitis. Computed tomography is not cost-effective. A positive result of biochemical tests despite a negative finding in US calls for an intensive search for gallstones by further investigation with endoscopic retrograde cholangiography or repeated US examinations.