Abstract: The present invention relates to a pharmaceutical formulation comprising (i) a therapeutically effective amount of a bispecific protein comprising a soluble T cell receptor (TCR) and an scFV; and (ii) a surfactant. The w/w ratio of surfactant to protein is in the range of 0.75:1 to 1.5:1. The formulation may further comprise a bulking agent and/or a stabiliser. A further pharmaceutical formulation comprises (i) a therapeutically effective amount of a bispecific protein comprising a soluble T cell receptor (TCR) and an scFV; (ii) a bulking agent; and (iii) a stabiliser. The w/w ratio of stabiliser to bulking agent may be greater than 1:1.