Empirical models of zooplankton biomass (rotifer, crustacean, and rotifer + crustacean biomass) in relation to selected morphometric (depth, surface area, flushing rate, and watershed area) and chemical variables were developed for 20 Adirondack lakes. The chemical variables were selected to characterize acidity status (pH, acid neutralizing capacity, and aluminum concentrations), trophic status (total phosphorus, chlorophylla, phytoplankton biovolume, and Secchi depth), and humic influences (with dissolved organic carbon and color serving as surrogates of humic materials). Additional independent variables included major cations and anions (Ca++, Mg++, Na+, K+, Cl−, and SO4−), specific conductance, dissolved oxygen, and temperature. Zooplankton biomass averaged 85.2 mg/m3in the study lakes. Crustacean biomass accounted for an average of 65.9 mg/m3and rotifer biomass for 19.4 mg/m3. Rotifer biomass was a significant component of zooplankton biomass in many circumneutral as well as acidic Adirondack lakes. The relative importance of rotifer biomass–as a percentage of total zooplankton biomass–could be predicted from an empirical relationship including the log of chlorophylla, the log of monomeric aluminum, and true color as independent variables (R2= .70). Rotifer biomass was particularly important in acidic lakes largely as a result of crustacean zooplankton loss rather than enhanced rotifer biomass. The best fit rotifer biomass empirical model included the log of total phosphorus and maximum depth as predictor variables (R2= .69). Crustacean biomass was best described by a relationship that included the log of monomeric aluminum, the log of chlorophylla, and the log of dissolved organic carbon (R2= .70). The best fit empirical model for total zooplankton biomass was a combination of the above models including all the above independent variables except total phosphorus. This model, reflecting the interactions of acidity and productivity status and humic influences, accounted for 74 percent of the lake to lake variability in mean zooplankton biomass.