The majority of anion transport inhibitors tend to be non-specific. This is problematic from a research point of view as caution is required when defining pathways purely based on pharmacology. Here we have tested a range of classical and putative Cl(-) transport inhibitors on three Cl(-) carrier systems (the KCl cotransporter (KCC), the NaK2Cl cotransporter (NKCC), and the Band 3 anion exchanger (AE)) found in human erythrocytes, using radiolabel tracer experiments. The study confirms the cross-reactivity of many anion transport inhibitors. However, two compounds, H25 and H156, were found to be both potent (IC(50) values < 0.1 mM) and specific (at least 1000-fold more effective against one carrier compared to the other two) inhibitors of NKCC and AE, respectively.