In 2003, Lange completed a study on the children of HIV-positive volunteer mothers in Rwanda and Uganda. He found that a baby's chance of contracting HIV falls to less than 1% if they receive anti-retroviral drugs while being nursed. The findings of the study were announced by Lange at the 2003 International AIDS Society meeting in Paris. During the 10th Conference on Retroviruses and Opportunistic Infections in Boston, Lange announced the results of a large multicenter clinical trial with the involvement of 1,216 patients in 17 countries. According to Lange, who served as principal investigator, these findings "clearly demonstrate the comparable efficacy of nevirapine and efavirenz in HIV treatment".