A procedure was developed for rearing larvae of Douglas fir tussock moth, Hemerocampa pseudotsugata McDun-nough, in large numbers on a synthetic medium for use laboratory testing of insecticides. The insect was reared from the egg stage generally to the fourth to seventh in-star, depending on testing needs. The larvae appeared normal in every way, reaching a weight of about 300 mg before pupation. An initial high loss from a nuclear polyhedrosis virus in the third instal was avoided by soaking the eggs in a 10% formaldehyde solution. Mortality during the larval stage on media was about 10%. Three thousand larvae were reared per week at a cost (excluding overhead) of about $15. At least 25,000 larvae could be reared weekly by I person working full time.