A number of vital life processes of an estuarine mysid (Mysidopsis bahia) were examined throughout its life cycle during exposure to the thiocarbamate herbicide, thiobencarb. Initial exposure of juvenile mysids to thiobencarb resulted in elevated respiration rates. Concentrations of thiobencarb that produced significant reductions in population survival through a complete life cycle (in approximately 24 days) significantly stimulated respiration rates of juveniles after only 4 days of exposure. Increased metabolic demands with sublethal thiobencarb exposure reduced the amount of assimilated energy available for production of new tissue by juvenile mysids, resulting in retarded juvenile growth rates. Higher O:N ratios during the maturation of thiobencarb-exposed mysids suggest a greater reliance on the more energy-rich lipid substrates in order to support the elevated rates of oxidative metabolism, resulting in less lipid material being available for gamete production.