OBJECTIVE To study the association of two polymorphisms of alpha-2 macroglobulin gene (A2M), a 1000G/A in exon 24 and a pentanucleotide insertion/deletion (I/D) in the 5'splice site in exon 18, with Parkinson's disease (PD) and essential tremor (ET) in North China. METHODS Using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method to investigate 87 cases of Parkinson's disease (PD),73 cases of ET and 100 randomly selected healthy control subjects. RESULTS (1) The allelic and genotypic distributions of A2M G/A were significantly different among the PD, ET patients and controls (P<0.05). The allele G and genotype GA in PD patients were significantly higher than those in ET patients or controls (P<0.05). There was no statistically significant difference between ET patients and controls in allelic and genotypic distribution (P>0.05). (2) The differences in allelic and genotypic distributions of A2M I/D among PD, ET patients and selected controls were found to be of no statistical significance (P>0.05). CONCLUSIONS (1) The polymorphism at the site of G/A might be associated with PD, but there might be no genetic association of polymorphism at this site with ET. (2) There might be no association of polymorphism at the site of I/D with PD and ET in North China.