Statement of problem: Provisional crowns cemented with provisional luting agents are susceptible to washout, marginal leakage, and secondary caries when placed for a prolonged period. Purpose: The purpose of this study was to examine the effect of incorporating chlorhexidine diacetate (antibacterial agent) into provisional cements on retention and marginal leakage of provisional crowns in vitro. Material and methods: Provisional crowns of acrylic resin (Duralay) were fabricated for 12 intact human molars with rounded-shoulder preparations. The 12 provisional crowns were luted individually with Temp Bond, Temp Bond NE, and Freegenol provisional cements with and without incorporation of chlorhexidine diacetate (CHDA) salt. Each test group included the same 12 specimens. Specimens with no luting agent served as the control (n=12). Specimens were thermal cycled 100 times (5°C and 55°C) with a 10-second dwell time, stored in 100% humidity at 37°C for 6 days, and then immersed in a 0.5% basic fuchsin at 37°C for 6 hours. Seven days after cementation, removal test of the crowns (tensile retention test) was conducted with a universal testing machine at a crosshead speed of 5 mm/min. Marginal leakage was assessed with a 5-level dye penetration scale. Results of the retention test were subjected to a 2-way ANOVA with repeated measures. A Bonferroni test was used to compare the means. Marginal leakage data were subjected to a nonparametric Wilcoxon signed ranks test. All hypothesis testing was conducted at the 95% level of confidence. Results: Retention of provisional crowns cemented with Freegenol enriched with CHDA increased 3-fold to an average level of 80.9 N. However, incorporation of CHDA into Temp Bond or Temp Bond NE did not affect retention. CHDA incorporated into the cements had no significant effect on the marginal leakage of all the tested cements. Conclusions: The addition of CHDA increased retention of Freegenol and had no significant effect on the marginal leakage of the tested cements. (J Prosthet Dent 2007; 98:373-378).