Aim: The aim of this in vitro study was to determine if accelerating the setting time of mineral trioxide aggregate, without altering its physical properties, would improve clinical efficiency. This involved examining whether the setting expansion of ProRoot MTA (Dentsply Tulsa Dental Specialities, Tulsa, OK, USA) was affected by adding an accelerant, 5% calcium chloride (CaCl2) and to investigate the setting expansion of a Portland cement clinker (PCC) mixed with a super plasticiser, 5.0 µl Glenium 7710 (SP). Materials and methods: Thirty-six samples were randomly divided into six groups: Groups 1 and 2 - grey and white MTA (GMTA, WMTA) prepared according to manufacturer's directions; Groups 3 and 4 - GMTA and WMTA mixed with water and accelerant; Group 5 - Type I Portland cement (PC) mixed with water; Group 6 - PCC mixed with water and SP. Each sample was vibrated into a 10 mm cylindrical mould and submerged in Hank's Balanced Salt Solution to simulate a physiologic environment. A linear variable displacement transformer dilatometer, accurate to 0.002%, measured setting expansion over a 24-hour period. A one-way ANOVA and a Tukey post hoc test (α = 0.05) were used to analyse the data. Results: A highly significant difference in expansion was found between the GMTA groups and all other groups (P = 0.001). There were no significant differences between the grey accelerated and nonaccelerated MTA groups, or between the white accelerated and non-accelerated MTA groups. The PCC with SP expanded significantly less than the GMTA groups but similarly to the WMTA groups. Conclusion: The setting expansion of MTA was not affected by adding an accelerant. Schlagwörter: accelerant, calcium chloride, expansion, MTA