In order to test the degree of concordance between ballpoint pen and palpation methods of measuring the skin induration after a Mantoux tuberculin test, we conducted a prospective, double-blind study. We performed a Mantoux skin test in 1,340 healthy subjects, aged 18 to 25 years, using the tuberculin PPD-RT 23, dose 2 IU, (1/5,000), of the Pasteur Institute, equivalent to 5 TU PPD-S. The same experienced reader, who was able to see only the site of the test (forearm), measured the induration after 48 hours by the palpation method, initially, and by the pen method later the same day, without knowing the identity of the examined person. Results of the study did not show any significant difference in any range of the measurements (p greater than 0.1) by the two methods. We conclude that the pen method is as reliable as the traditional palpation method. The sensitivity and the specificity of the two methods are comparable. Even though our study was not designed to investigate the effects with an inexperienced examiner, given the simplicity of the pen method, it could be the method of choice, especially for less experienced examiners.