Setting time of mortar incorporating both silica fume and superplasticizer in varying amounts is observed to be a function of temperature and composition. Temperature effects are shown to be predictable using conventional maturity techniques. Reductions in cement content and increases in superplasticizer dosage tend to retard setting, while increases in silica fume content tend to accelerate setting. Adjustment factors are developed which enable prediction of initial set time as a function of composition. Practical applications are suggested.