The regulation of JH epoxide hydrolase, JH esterase and 1-naphthyl acetate (NA) esterase activity was studied in ovary, gut, head and carcass after blood feeding in Culex quinquefasciatus. The combined tissues had the greatest JH epoxide hydrolase and JH esterase activity from 24-36 hr after a blood meal. JH epoxide hydrolase activity per female was 2.1-, 1.8- and 1.1-times greater than the JH esterase activity at 24, 36 and 48 hr after blood feeding, respectively. JH epoxide hydrolase activity per until protein was also the major route of primary JH metabolism at most time points examined, and peak JH epoxide hydrolase activity per unit protein in the gut, head and carcass was approximately 2-5 times the highest JH esterase activity per unit protein in corresponding tissues and 4-times the peak JH esterase activity in the ovary. The differential expression of JH epoxide hydrolase versus JH esterase in specific tissues and between tissues suggested that regulation of JH metabolism is tissue specific. Two isoelectric forms of JH esterase were found. The juvenoid, (RS)-methoprene, interfered with the regulation of JH esterase activity, but failed to change the activity levels of JH epoxide hydrolase and 1-NA esterase.