The aims of this study were to compare the minimum inhibitory concentration level of tetracycline hydrochloride (TC) in gingival crevicular fluid (GCF) after single pocket irrigation with 5% and 10% concentrations at different time intervals. The subjects were systemic tetracycline within the past 6 months. The studied sites were the tooth surfaces having pockets 5-7 millimeters (the mean pocket depth is 5.11 millimeters). Two hundreds sites were divided into two groups: one group using 5% and another 10% TC (w/v, 15 ml, 5 min/site). The GCF samples were collected on paper strips at the time intervals, 1 hour, 1, 3, 5 and 7 days after pocket irrigation. The TC in each strip was eluted and analysed by high performance liquid chromatography. The results showed that the ratained TC concentration in GCF from both groups were not statistically different at 1 hour, level (MIC=8 µg/ml) up to 5 days (p<0.05). At 7 days after pocket irrigation, the TC concentrations in GCF was significantly higher (p<0.05) in the 10% TC group (10.13 ±1.77 µg/ml) than in the 5% TC group (5.41±0.84 µg/ml).The aims of this study were to compare the minimum inhibitory concentration level of tetracycline hydrochloride (TC) in gingival crevicular fluid (GCF) after single pocket irrigation with 5% and 10% concentrations at different time intervals. The subjects were systemic tetracycline within the past 6 months. The studied sites were the tooth surfaces having pockets 5-7 millimeters (the mean pocket depth is 5.11 millimeters). Two hundreds sites were divided into two groups: one group using 5% and another 10% TC (w/v, 15 ml, 5 min/site). The GCF samples were collected on paper strips at the time intervals, 1 hour, 1, 3, 5 and 7 days after pocket irrigation. The TC in each strip was eluted and analysed by high performance liquid chromatography. The results showed that the ratained TC concentration in GCF from both groups were not statistically different at 1 hour, level (MIC=8 µg/ml) up to 5 days (p<0.05). At 7 days after pocket irrigation, the TC concentrations in GCF was significantly higher (p<0.05) in the 10% TC group (10.13 ±1.77 µg/ml) than in the 5% TC group (5.41±0.84 µg/ml).