BACKGROUND There are several brands of fluoride varnishes in the market, but the dynamics of fluoride release from each one might be different. The purpose of this study was to evaluate in vitro the release of fluorides by fluoride varnishes and to determine the correlation with viscosity and wettability. METHODS Forty four enamel blocks 5x5 mm were randomly divided into 4 groups (n=11) ((Duraphat®, Clinpro™ White Varnish, Flúor Protector® and control). We applied 30 milligrams of fluoride varnish to each specimen. The specimens were immersed in a Calcium Phosphate solution at a pH= 6.0. We evaluated the release of fluoride, by using a selective fluoride electrode, during 6 weeks. Viscosity was measured using an Oswald Viscosimeter and the wettability was determined by measuring the contact angle between the varnish and the enamel slab. The statistical analysis was performed using Analysis of variance. RESULTS Duraphat showed the highest fluoride release from the second weekend beyond (p<0.001) and Clinpro the greatest rate of release. Duraphat release was the steadiest throughout the experiment. Duraphat showed the highest viscosity and the lowest wettability (p<0.001) and Fluor Protector showed the highest wettability (p<0.001). There was a positive correlation between the release of fluoride and the viscosity and a negative correlation between fluoride release and wettability (r>0.7). CONCLUSIONS Viscosity and wettability influence the release of fluoride from fluoride varnishes. Key words:Fluorides topical, viscosity, wettability.