OBJECTIVE Widely used in caries prevention, fluoridated varnish (FV) is also capable of remineralising carious lesions. However, the retention time of FV needed on enamel to ensure the maximum benefit is unclear. This study aimed to determine whether an increase in the retention time of 5% sodium fluoride (NaF) varnishes on enamel carious lesions enhances remineralisation. METHODS Carious lesions were generated on bovine enamel slabs and treated with one of three 5% NaF commercial varnishes: Duraphat, Durashield or FlorOpal. After application, the varnishes were maintained on the slabs for 8, 12, 18, 24, 36 or 48 h while immersed in artificial saliva. Remineralisation efficacy was calculated and expressed as the percentage of surface microhardness recovery (%SHR). Untreated carious lesions served as negative controls. Data from each timepoint for each product were compared by ANOVA, followed by a post-hoc test (p < 0.05). RESULTS There was a trend for increased remineralisation over time, reaching maximum %SHR values of about 30% after 18 to 24 h. No significant differences were detected after 18 h (p > 0.05). This remineralisation dynamic was similar among the three tested products. CONCLUSIONS Remineralisation of enamel lesions using 5% NaF varnish appears to be initially dependent on the retention time of the product. Higher remineralisation was observed upon 18 h of varnish retention on the lesions.