Collagenolysis in periodontitis is thought to be modulated by the expression of three genes, collagenase, tissue inhibitors of metalloproteinases-1 and -2 (TIMP-1 and -2). We assessed the possible difference in TIMP-1, TIMP-2 and collagenase mRNA levels between gingival samples from patients with periodontitis and those from healthy subjects by reverse transcription-polymerase chain reaction (RT-PCR). This technique allows detection of transcripts from a very small sample quantity. The experiments showed that levels of TIMP-1 and collagenase transcripts relative to beta-actin are significantly higher in the diseased group than in healthy controls (8.11 +/- 0.83 versus 1.38 +/- 0.28% for TIMP-1 and 0.50 +/- 0.10 versus 0.0075 +/- 0.0024% for collagenase, respectively). The difference in TIMP-2 between the two groups (2.91 +/- 0.46 versus 1.84 +/- 0.87%) did not differ. Therefore, the host would have responded to the increase in collagenase level by preferentially producing TIMP-1 against tissue destruction. The differential gene expression of TIMP-1 and TIMP-2 in our study may account for a distinct genetic regulation of TIMP-1 and -2 in vivo.