Abstract:The tissue reactivity of a monoclonal antibody raised against human granulocytes, FMC 34, was shown to overlap with antibodies including FMC 10, which is directed against the X‐hapten, and with T5A7, which is directed against lactose‐bearing antigens. Reactivity of FMC 34 on sections of human cornea was more widespread than that of either FMC 10 or T5A7. High sensitivity fluorescence testing revealed that both FMC 34 and T5A7reacted weakly with the T‐lymphocyte cell line JM, unlike the CD 15 antibody FMC 10. Competitive binding experiments showed that binding of FMC 34 to granulocytes was inhibited by preincubation with T5A7, while FMC 34 itself was able to inhibit the binding of both FMC 10 and T5A7. The binding of FMC 10 was not inhibited by preincubation of cells with T5A7. Saturation‐binding analyses revealed that each human granulocyte could bind 17.5 × 105molecyles of FMC 34, which was more than three times the number of molecules of FMC 10 which could be bound to each cell. The additional reactivity of FMC 34 appears to be due to its capacity to bind fucosylated and non‐fucosylated lactose‐bearin