Background and Aims: To evaluate genotyping for two DNA variants (c.1993+ 327C > T and c.1438+ 117G >A), recently found to be associated with adult-type hypolactasia, in the diagnosis of lactose intolerance. Methods: In total, 166 consecutive patients with gastrointestinal symptoms mimicking hypolactasia admitted to the clinic between March 2002 and December 2002 were included. Genotyping for the two DNA variants (c.1993+ 327C > T and c.1438+ 117G > A) and standard H2 breath test was performed. Results: Among 116 patients with positive H2 breath test, the c.1993+ 327C variant was detectable in 106 (91.4% ) patients. Among 50 patients with negative H2 breath test, the c.1993+ 327C variant was seen in 2 patients. Sensitivity, specificity, positive and negative predictive values for the c.1993+ 327C variant were 91.4, 96.0, 98.1 and 82.8% , respectively. Genotyping for the c.1438+ 117G variant did not bring any additional information. Among 4 of the 10 patients with positive H2 breath test but negative for the c.1993+ 327C and the c.1438+ 117G variant, further evaluation revealed other diseases known to cause secondary hypolactasia such as celiac disease and short bowel syndrome. Conclusion: In symptomatic patients, genotyping for the DNA variant c.1993+ 327C is a reliable test for adult- type hypolactasia with high sensitivity and specificity and thus provides a new tool in the diagnostic workup of hypolactasia. Background and Aims: To evaluate genotyping for two DNA variants (c.1993 + 327C> T and c.1438 + 117G> A), recently found to be associated with adult-type hypolactasia, in the diagnosis of lactose intolerance. Methods: In total, 166 consecutive patients with gastrointestinal symptoms mimicking hypolactasia admitted to the clinic between March 2002 and December 2002 were included. Genotyping for the two DNA variants (c.1993 + 327C> T and c.1438 + 117G> A) and standard H2 breath Among the 50 patients with positive H2 breath test, the c.1993 + 327C variant was detectable in 106 (91.4%) patients. Among 50 patients with negative H2 breath test, the c.1993 + 327C variant was seen in 2 patients. Sensitivity, specificity, positive and negative predictive values ​​for the c.1993 + 327C variant were 91.4, 96.0, 98.1 and 82.8%, respectively. Genotyping for the c.1438 + 117G variant did not bring any additional information. Among 4 of the 10 patients with positive H2 breath tes t but negative for the c.1993 + 327C and the c.1438 + 117G variant, further evaluation revealed other diseases known to cause secondary hypolactasia such as celiac disease and short bowel syndrome. Conclusion: In symptomatic patients, genotyping for the DNA variant c .1993 + 327C is a reliable test for adult-type hypolactasia with high sensitivity and specificity and there provide a new tool in the diagnostic workup of hypolactasia.