1. Investigations were made of the effect of various procedures in raising or lowering the microfilaria count of Pacific type Wuchereria bancrofti in the peripheral blood.
2. Raising the body temperature in the early morning was followed by a moderate fall in the counts. Breathing increased oxygen, or reduced oxygen (hypoxia) or increased carbon dioxide, or the ingestion of sodium bicarbonate produced no consistent and significant changes in the count. Ingestion of glucose (in one volunteer) was followed by a small rise in the count. Muscular exercise was followed by a fall in the count, which is interpreted as probably being a response to a lower concentration of oxygen in the venous blood returning to the lung.
3. It has not been possible to identify the physiological components of the circadian rhythm of the human body which entrain the cycle of these microfilariae. Attempts to obtain evidence incriminating the stimuli described above have been unsuccessful.