Objectives: aim of study-to compare effects of two chlorhexidine-gels delivered into periodontal pockets during initial periodontal therapy. Methods: Fifty-one patients(32male,19female) with periodontitis, displaying pockets 5 mm underwent periodontal examination at baseline and after four weeks: assessment of PI, BOP, PD, CAL at six sites/tooth. Maximal-values/quadrant and mean-overall-values of PD+CAL were considered. Patients received initial therapy according to the one-stage-Full-Mouth-Disinfection(Quirynen, 1995). Each quadrant of same-arch randomly received single subgingival application of novel chlorhexidine-xanthan-based-gel(Chlosite®,Ghimas,Italy) or chlorhexidine-gel PlakOut®,(Santa-Balanos,Greece). Patients used 0,2%chlorhexidine mouthwashes(Dentaton®,Ghimas,Italy),for following four weeks, OHI were reinforced. Wilcoxon test was used to compare differences between baseline and four weeks after, and differences between groups. Results: Both therapies resulted in significant improvements in all indices. At four weeks, in the "maximal-values/quadrant" data-group of Chlosite-treatment group, meanPD changed from 8.90±2.26 to 5.25±1.90(pConclusions: Following both approaches, there were significant clinical improvements. Additional single-topical subgingival-application of Chlosite was safe, providing more favorable CALgain and PDreduction than PlakOut. Keywords: periodontal non-surgical therapy, chlorhexidine xanthane based gel, split-mouth study