For 207 women participating in a zinc supplementation trial in Lima, Peru, we used multiple regression techniques to identify maternal socioeconomic, health and nutritional factors influencing serum zinc concentrations at baseline, when women entered prenatal care between 1024 wks gestation. Serum zinc concentrations (/imol/L) declined with increasing wks of gestation, from 12.8 ±2.2 at 10 wks, to 10.1 ±1.2 at 18 wks, to 9.9 ±1.6 at 24 wks gestation. After adjusting for duration of pregnancy, variation in serum zinc concentration was associated (at P< 0.05) positively with better household sanitation facilities and maternal height, and negatively with maternal age. Body mass index (BMI), and various skinfold thickness measures (triceps, sub-scapular and calf) were each positively associated with, and equally predictive of, serum zinc levels, whereas mid-upper arm and calf circumferences were not important factors. The results suggest that maternal socioeconomic and nutritional factors are related to serum zinc concentrations, and in particular highlight the potential role of fat stores in determining serum, zinc concentrations during pregnancy. (Supported by USAID DAN-5116-A-00-8051-00).