35 cases of lepromatous and near-lepromatous cases of laprosy in Reaction have been investigated for the presence of acid-fast bacilli in blood at the height of the reaction as well as at its subsidence. Only 3 cases exhibited bacillaemia during reaction. It is therefore unlikely that dissemination of the disease is accentuated during reaction as commonly believed. Further, the immune complexes demonstrated to be circulating during reaction are possibly formed by bacillary products and not by whole or fragmented bacilli.