Twelve out of 14 strains of Pseudomonas pseudomallei were inhibited in vitro by a combination of trimethoprim 1 mug per ml and sulphamethoxazole 20 mug per ml or by lower concentrations. Of the remaining strains, one was marginally more resistant and one was distinctly so. In tests utilizing two of the sensitive strains, inhibitory concentrations of the individual drugs exerted a bactericidal effect when combined.