Structural analogues of a sulphated polysaccharide, dextrin sulphate, were synthesized and tested for their ability to block infection by HIV‐1. Using the T‐cell lines, C8166 and HPB‐ALL, and the laboratory adapted strains of HIV‐1.MN, HIV‐1.IIIb and HIV‐1.RF, dextrin 2‐sulphate (D2S) combined the best combination of high anti‐HIV‐1 activity (95% inhibitory concentration (IC95) = 230 nM) and low anticoagulant activity. It also blocked infection of activated peripheral blood mononuclear (PBMN) cells by five primary viral isolates at an IC95 of 230–3700 nM depending upon the primary viral isolate tested. In saturation binding studies, [3H]‐D2S bound to a cell surface protein on HPB‐ALL cells in a specific and saturable manner with a Kd of 82 ± 14 nM and a Bmax of 4.8 ± 0.3 pmol/106 cells. It bound to other human T‐cell lines in a similar manner. There was very little binding of [3H]‐D2S to freshly isolated PBMN cells (Bmax 0.18 ± 0.03 pmol/106 cells) and these cells could not be infected by HIV‐1. Culture of PBMN cells in lymphocyte growth medium (LGM) containing IL‐2 did not significantly change the Bmax of [3H]‐D2S. In contrast, PBMN cells which had been cultured with phytohaemagglutinin (PHA; 5 μg ml−1) for 72 h had a Bmax of [3H]‐D2S binding of 7.2 ± 0.1 pmol/106 cells and these cells could be infected by HIV‐1. Removal of the PHA and further culture of the PBMN cells in LGM containing IL‐2 resulted in a fall in the Bmax to 2.0 ± 0.1 pmol/106 cells. The Kd of binding did not change significantly during the course of these experiments. [3H]‐D2S did not bind to freshly isolated erythrocytes or to erythrocytes which had been cultured in PHA for 72 h. These results suggest that there is a relationship between the expression of the [3H]‐D2S binding protein on the plasma membrane of PBMN cells and the susceptibility of these cells to infection by HIV‐1.