The AMPFlSTR((R)) SGM Plus system is a commercially available STR multiplex produced by Applied Biosystems, a division of Perkin Elmer, Foster City, California, USA that supersedes SGM. The multiplex contains the six SGM loci, amelogenin and four additional loci. These additional loci are D3S1358, D19S433, D16S539 and D2S1338. Consequently, the match probability is significantly improved (conservatively quoted as 1 in 10(9) for reporting a full profile match). The system was subjected to validation. For example, ageing and degradation studies demonstrated semen stains to be the most stable evidence type, whereas buccal scrapes were the least stable. An apparent rise in the sensitivity increases the chance of obtaining successful results from the more difficult samples submitted for analysis. Two of the new loci (D3S1358 and D19S433) are low molecular weight (between 100 and 150 base pairs); this improved the success rates of the degraded samples where high molecular weight loci may drop out. Of 26 non-primates tested, four gave results that appeared as single peaks and were unlikely to cause interpretation problems. None of the 19 micro-organisms tested gave discernible results. Extensive casework and simulated casework studies demonstrated that SGM and SGM plus results were comparable. There was one example of a null allele (primer binding site mutation) recorded at the HUMFIBRA locus (in both systems). However, a concordance study of 1000 samples using both SGM and SGM plus did not demonstrate any differences in typing.