A processed bacteriological agar of very high working gel strength (1.5% w/v) which has low Ca and Mg levels. It is compatible with all culture media and it enables broth and agar formulations of the same medium to have very similar metal values. This characteristic is especially valuable in antimicrobial MIC studies where differences in mineral/metal content can profoundly influence the results. It is also a highly satisfactory agar for antimicrobial diffusion studies (disc diffusion susceptibility tests) because its low mineral/metal content allows free diffusion of antimicrobial substances.