Analysis of the effects of AZT and ddI treatment on drug-resistance in esophagus (E), stomach (S), duodenum (D), colon (C) and PBL (L). Resistance mutations were recorded and scored using the Stanford Drug-Resistance Database for level of drug-resistance. Sequences with intermediate to high-level resistance for AZT, or ddI were considered drug-resistant. The number of drug-resistance sequences recovered after AZT (A) or ddI (B) treatment in each tissue was expressed as the percentage of all sequences recovered from the tissue. Different numbers of AZT and ddI resistant sequences were found in the gut tissues and PBL following AZT treatment and ddI treatment, respectively (* p < 0.05, Pearson chi-square test)The average drug-resistance score for each drug also varied in each tissue. AZT drug resistance scores were the highest in the colon following AZT treatment (C). However, ddI resistance scores did not differ significantly in the different tissues following ddI treatment (D). These observations are consistent with differential distribution of antiretroviral drug-resistance in the gut, and indicated that the AZT and ddI treatment affected each tissue differently (* p < 0.05, Tukeys HSD post-hoc analysis).