: We investigated regularly swabs of adults dispenzarised at Mary Immaculate Clinic of Trnava University in Nairobi providing free health care for about 50 000 population of Mukuru Slums. 20 patients who were treated for AIDS by our clinic (those who started HAART before Free National AIDS Cooperation Programme - NASCOP) were assessed after 1, 2 and 3 years (18 of 20 completed the survey, other 2 loss of follow up, probably died. Exposure to other molecules can select resistant mutants. Previous exposure to TMP/SMX was similar in both groups and therefore was not responsible for the difference between resistance patterns.