METAL was written in C++ and is freely available for download. METAL compiles and runs on most Unix and Linux systems, and on Windows and Mac workstations. We recently performed a meta-analysis of GWAS for BMI (Willer et al., 2009). The analysis included 15 studies, each with association statistics at 2.2–2.5 million SNPs (average file size 225 MB), for a total of 36 million association statistics and a set of input files totaling 3.4 GB. This analysis required <6 min computing time and 790 MB of memory on a 2.83 GHz Intel processor. Runtime scales linearly with the number of studies examined—a meta-analysis including 74 input files (each with >2.5 m SNPs) took 36 min and 1 GB of memory.
