A prescale gel product, designed to facilitate the removal of calculus, has recently been introduced and marketed to the dental profession. The purpose of this study was to evaluate the effectiveness of this gel on the removal of subgingival calculus. 10 patients, each with 5 periodontally diseased teeth scheduled for extraction, participated in this in vivo/in vitro study. 4 teeth per patient were randomly assigned using a 2-by-2 block design and treated in vivo with either active or placebo gel, with or without scaling, prior to extraction. To assess possible overexposure to the product, 10 selected teeth from the sample were treated with active gel for an extended exposure time. Standardized scaling was performed on a 4x4 mm treated root area in vitro on groups as assigned. Quantification of residual calculus was determined by one examiner blind to treatment group assignment using SEM photomicrograph montages and the Java image analysis computer system. Repeated measures ANOVA showed no statistically significant treatment effect for gel (p > 0.05) in the scaled and no-scaled groups. The 5th group exposed to the prescale gel for an extended time was evaluated descriptively for root surface morphological changes with no noticeable effect. Based on the results of this investigation, treatment of subgingival calculus with prescale gel offers no advantage for calculus removal over scaling alone. The findings suggest no significant clinical impact of product use.