Hepatic hydroxysteroid sulfotransferase-a (HST-a) gene expression was examined in young male (age 22-26 days) and female rats (age 22-30 days), and in older male (age 42-45 days) and female (age 49-55 days) rats. Northern and slot blot analyses of poly(A)+RNA revealed that HST-a was differentially expressed with respect to both age and gender with female rats expressing higher levels of HST-a in both age groups. Hepatic HST-a mRNA levels were approximately 4 to 6-fold higher in females compared to males in both age groups examined. HST-a expression increased with age in both male and female rats. HST-a expression was approximately 8 to 10-fold higher in 42-45 day old males relative to 22-26 day old males. HST-a mRNA levels were approximately 3 to 7-fold higher in 49-55 day old females relative to females in the 22-30 day age group. These data suggest that HST-a gene expression is transcriptionally controlled and that HST-a regulation is subject to hormonal and developmental modulation.