As part of a systematic investigation of their use with Ciment Fondu, the rheology of pastes containing three superplasticizers is reported. The effects were not as dramatic as those observed with Portland cements, and at low concentrations the yield values and plastic viscosities were higher than in pastes without admixture. However, at 0·6% and 1% (dry weight of cement) a sulphonated phenol formaldehyde resin reduced these parameters for long enough to be of practical use. A naphthalene-type resin was effective over a shorter time, but pastes containing a melamine-type resin stiffened too rapidly to be useful. The stiffening was generally less rapid at 5°C than at 20°C, and is attributed to the precipitation of alumina gel in the paste.