TVV75, a strain of Burkholderia vietnamiensis, was isolated from an acid sulphate soil of south Vietnam, and selected for its high in vitro nitrogen fixation potential. This plant growth-promoting rhizobacterium (PGPR) had been used in a previously reported pot experiment. It was used in two new pot experiments and four field experiments to inoculate lowland rice at sowing and at transplanting, in three different South Vietnam acid sulphate soils. We first studied the effect of inoculation during early plant growth in nurseries. Seedlings were then transplanted both to field and pots. Treatments included two levels of inoculation (inoculated vs uninoculated) and three levels of N fertilizer (0, recommended rate and half this rate), in a randomized block design with six replicates. In all four experiments nitrogen appeared to be the limiting factor for yield. Inoculation had already had a strong beneficial effect at the transplanting stage (day 24), as measured by shoot weight (+33%) root weight (+57%), and leaf surface (+30% at day 14). Final results indicated that inoculation of rice with B. vietnamiensis TVV75 significantly increased several yield components, resulting in a final 13 to 22% increase in grain yield. A late yield component, 1,000 grain weight, was significantly increased by inoculation, but not by nitrogen fertilizers, in all pot and field experiments, indicating a long-lasting effect of the inoculated bacteria. It was possible to evaluate the nitrogen fertilizer equivalent of inoculation (NFEI): at the medium rate of N fertilizer, inoculation ensured a yield equivalent to that obtained in the uninoculated control with 25 to 30 kg more nitrogen fertilizer. Comparison of the local cost of NFEI kg N-fertilizer and the cost of inoculation would help in making the decision to inoculate.