Sensitivity of HIV-1 R5 envelopes to reagents that target gp41 and inhibit conformational changes in gp41 required for fusion. Pseudovirions carrying envelopes encoded by envelope genes amplified from patient samples were tested for sensitivity to inhibition by (A) mab 2F5, (B) mab 4E10 and (C) T20. Macrophage-tropic envelopes (light symbols) and non-macrophage-tropic envelopes (dark symbols) were examined. Statistical analysis showed no overall correlation between macrophage-tropism and sensitivity to 2F5, 4E10 or T20. However, when just brain and lymph node envelopes were evaluated, a correlation between macrophage-tropism and increased sensitivity to T20 was nearly reached (p = 0.0658).