Mutations in the DJ-1 gene have been implicated in the PARK7-linked autosomal recessive form of Parkinson's disease (PD). The molecular properties of DJ-1 WT, DJ-1 L166P, and a newly identified disease-causing mutant DJ-1 M26I were explored after they were transiently expressed in mammalian cells. Treatment of intact, living cells with the chemical crosslinker disuccinimidyl suberate (DSS) revealed that DJ-1 WT and mutant DJ-1 M26I were present as stable homodimers; DJ-1 L166P in particular tended to form high-order complexes as well. In contrast to DJ-1 L166P that is quickly degraded by the proteasome, DJ-1 M26I was found to be an efficiently expressed and stable variant of DJ-1, suggesting that these mutations have distinct biochemical effects on DJ-1. We further provide evidence that in human brain, under nondenaturing conditions, DJ-1 is present in high molecular weight (HMW) complexes of approximately 250-700 kDa containing parkin, another PD-associated protein.