Objective To observe the change of the salivary occult blood after periodontal mechanical therapy,and to assess the correlations between salivary occult blood and the level of volatile sulphur compounds (VSC) in oral cavity,periodontal clinical parameters,respectively.Methods Fifty patients with gingivititis,mild or moderate periodontitis were included.The level of VSC were measured by Halimeter(R) and salivary occult blood was tested by Periosereen(R) before periodontal examination.Then full mouth plaque index (PLI),probing depth (PD),bleeding index (BI) were charted.Attachment loss (AL) of the Ramfj(o)rd teeth were recorded lastly.Intensive periodontal mechanical therapy was conducted including oral hygiene instruction,scaling and root planing(SRP).Four weeks after SRP,the same examinations were repeated.Results Salivary occult blood was significantly correlated with BI (r = 0.294) and PLI (r =0.308) before periodontal therapy (P < 0.01),and also significantly correlated with VSC level (r = 0.386),PLI (r = 0.456),BI (r = 0.352),AL(r = 0.325) after therapy (P < 0.05).The improvement of VSC level [211.0(111.0-389.5)×10-9 vs 100.0(46.3～165.3)× 10-9],the clinical periodontal parameters including PLI[(1.3 ±1.0) vs (0.4±0.6)],PD[(3.7±l.5)mmvs (2.7±0.9)mm],BI[(1.8±1.2)vs (0.4±0.7) ]and AL[(1.0± 1.1)mm vs (0.1±0.5) mm after the treatment was statistically singnificant(P <0.001).However,standing on the viewpoint of salivary occult blood changes from positive before therapy to negative after therapy,only 80% (40/50) individuals were totally cured.VSC level in oral cavity and periodontal clinical parameters significantly decreased (P < 0.001) following the trends from strong positive,weak positive,to negative results of salivary occult blood test .Condnsions Salivary occult blood was correlated with VSC level in oral cavity of periodontal treated patients.It may be an objective parameter to evaluate the gingival inflammation and the efficacy of the periodontal therapy at individual level.