Precultivated autologous macrophages enhanced the early PPD‐induced blastogenic response of tuberculin‐sensitive lymphocytes. This effect was not caused by a diffusible macrophage product. Macrophages exposed to PPD and subsequently washed caused as high a response as did PPD in cultures without precultivated macrophages. Sensitive macrophages were not able to induce nonsensitive lymphocytes to respond to PPD. Precultivated macrophages from tuberculin‐negative patients with sarcoidosis enhanced the PPD‐induced transformation of sensitive lymphocytes, as did autologous macrophages Cord blood‐derived macrophages were significantly less