Abstract While a great deal of work has been reported on innate and adaptive white blood cells infiltrating solid tumors, as well as the pre-metastatic niche, there is a paucity of information concerning the early innate immune response to primary tumors. This is particularly evident in the very early stages; before a solid tumor is palpable. Here we used a gelatin sponge model to investigate white blood cells infiltrating a tumor site 12–72 hours following injection. Initial studies focused on identifying the total number of infiltrating cells as well as the number of lymphocytes, macrophages and granulocytes. While 12 hours after injection there was no difference in the total number of cells infiltrating the tumor site versus a control site injected with saline, at 24 and 48 hours there was a small, yet significant increase in the number of cells at the tumor site. The majority of the cells to arrive at the tumor and saline injected sites within the first 12 hours were Gr1+F4/80+ (60%), and this population of cells decreased to 36% by 72 hours at both sites. These data contrasted with the F4/80+Gr1− cells which increased over time from about 10% at 12 hours to 25% at 72 hours. Moreover, two significant differences were noted between the tumor and saline sites. At 24 hours there were significantly more F4/80+Gr1-cells at the tumor site, and the number of Gr1+F4/80− cells remained higher at the tumor site over time. These data indicate early macrophage recruitment and neutrophil retention at the primary tumor site. Gene expression analysis by quantitative RT-PCR is underway to investigate additional differences in these cell populations.