The GSK-3β gene, GSK3B, codes for an enzyme that is a target for the action of mood stabilizers, lithium and possibly valproic acid.In this study, the relationship between haplotypes consisting of single nucleotide polymorphisms (SNPs) of GSK3B -50T/C and -1727A/T and the effect of lithium was studied among Japanese bipolar disorder lithium nonresponders and responders.The distributions of the GSK3B haplotypes (-50T/C and -1727A/T) showed a trend for significant difference between the lithium nonresponders and responders (global P=0.07074). Haplotype 1 (T-A) was associated with a higher lithium response (haplotype-specific P=0.03477), whereas haplotype 2 (C-A) was associated with a lower lithium response (haplotype-specific P=0.03443).The pairwise D' and r values between the 2 SNPs in this study were 1.0 and 0.097, respectively. The 2 SNPs showed weak linkage disequilibrium with each other.