AIMS--To detect HLA susceptibility and protective alleles associated with insulin dependent diabetes mellitus (IDDM) using a multiplex amplification refractory mutation system (ARMS). These include DR3 and DR4 alleles at the DRB1 locus, presence or absence of aspartic acid at position 57 (Asp-57) of the DQB1 locus, and presence or absence of arginine at position 52 (Arg-52) of the DQA1 locus. METHODS--The ARMS approach was used to design allele specific primers for the detection of the major susceptibility and protective alleles for IDDM. These include DR3 and DR4 alleles at the DRB1 locus, Asp-57 and non-Asp-57 at the DQB1 locus, and Arg-52 and non-Arg-52 alleles at the DQA1 locus. The allele specificity of each set of primers was first tested separately using DNA samples from 15 individuals previously typed for the DRB1, DQB1, and DQA1 loci using the sequence specific oligonucleotide (SSO) technique. The possibility of using multiplex ARMS for typing multiple susceptibility/protective alleles for IDDM was further investigated by testing various combinations of allele specific primers, thereby reducing the number of separate polymerase chain reactions required to type all these alleles. RESULTS--A "three-tube" system worked well and gave accurate results. Tube 1 contained ARMS primers for the detection of IDDM susceptibility alleles DR3 and DR4; tube 2 contained ARMS primers for the detection of susceptibility alleles non-Asp-57 and Arg-52; and tube 3 contained ARMS primers for the detection of the protective alleles Asp-57 and non-Arg-52. DNA samples typed with this ARMS method were in complete agreement with those obtained using the SSO technique. CONCLUSION--This method is rapid and has no requirement for radioactivity. It is an efficient method for population screening.