The response of the Mi-1 gene to different densities of Meloidogyne incognita race 2 was investigated under controlled conditions. Susceptible and resistant tomato seedlings were inoculated with 25, 50, 100, 200, 400, 1000, 2000, 5000 and 10000 second-stage juveniles of M. incognita. Plants were uprooted 8 weeks after inoculation and the numbers of egg masses and galls on the roots, and second-stage juveniles in 100 g soil per pot were counted. In susceptible plants, there was a correlation between the number of egg masses on roots until 2000 J2 inoculum densities. In resistant plants, when inoculum densities increased, the number of egg masses and galls also increased. The reproduction factor ratio was >1 in the susceptible plant and <1 in the resistant plant. The data showed that the 5000 J2 inoculum was a critical limit, and 10000 J2s were above threshold for resistant plants. The data indicate that densities of M. incognita can seriously affect the performance of the Mi-1 gene.