The serine protease inhibitor Kazal type 1 (SPINK1), also known as pancreatic secretory trypsin inhibitor (PSTI), is a peptide secreted by pancreatic acinar cells. Genetic studies have shown an association between SPINK1 gene variants and chronic pancreatitis or recurrent acute pancreatitis. The aim of this study was to clarify whether the SPINK1 variants affect the level of serum PSTI.One hundred sixty-three patients with chronic pancreatitis or recurrent acute pancreatitis and 73 healthy controls were recruited. Serum PSTI concentrations were determined with a commercial radioimmunoassay kit.Ten patients with the p.N34S variant, 7 with the IVS3+2T>C variant, two with both the p.N34S and the IVS3+2T>C variants, and one with the novel missense p.P45S variant in the SPINK1 gene were identified. The serum PSTI level in patients with no SPINK1 variants was 14.3 ± 9.6 ng/ml (mean ± SD), and that in healthy controls was 10.7 ± 2.2 ng/ml. The PSTI level in patients carrying the IVS3+2T>C variant (5.1 ± 3.4 ng/ml), but not in those with the p.N34S variant (8.9 ± 3.5 ng/ml), was significantly lower than that in the patients without the SPINK1 variants and the healthy controls. The serum PSTI level in the patient with the p.P45S variant was 4.9 ng/ml. Low levels of serum PSTI (C and p.P45S carriers from non-carriers.Serum PSTI levels were decreased in patients with the IVS3+2T>C and p.P45S variants of the SPINK1 gene.