The main equilibria present in dilute and concentrated HF solutions (up to 2 mol l(-1)) in ethanol + water 93:7 by volume are studied. This particular medium is interesting because it is used to clean silica surfaces in semiconductor technology. Conductometric and potentiometric (glass electrode and fluoride-ion-selective electrode) techniques are used to demonstrate that formation of HF and HF2- predominates in dilute HF solutions, whereas HF and polyhomoconjugated species predominate in concentrated HF solutions. The constants of these equilibria are determined.