Bismuth sulphite agar is by far the most efficient of all single media devised for the isolation of typhoid bacilli from stools. When tested in comparison with other media it was found not only to afford the highest percentage of positive results but also the maximum inhibition of saprophytic growth. Its remarkable selectivity is demonstrated by the fact that negative plates are often completely sterile, and positive ones often consist exclusively of typhoid colonies (Loureiro & Matos, unpublished observations).