Steroidal estrogens and antibiotics used in veterinary and human medicine are detected in livestock manure or sewage sludge and biosolids. Biodegradation is an important process by which estrogenic compounds are removed from organic amendments, but antibiotics have been shown to impede microbial communities. Although both compounds are often present in these media, the fate of estrogens in association with antibiotics has not been previously studied. In this study, both rates of tetracycline (40 and 200 mg kg-1) in liquid swine manure induced a lag phase of 40 to 50 days prior to the onset of a log phase of estrone and 17 β-estradiol mineralization, and tetracycline at 200 mg kg-1 significantly reduced maximum mineralization of estrone and 17 β-estradiol in manure. In soils amended with a high rate of manure, penicillin at 200 mg kg1 also significantly decreased maximum mineralization of estrone and 17 β-estradiol relative to soils free of antibiotics. Estrogen mineralization almost always significantly decreased in the order of: manure > soil amended with a low rate of manure = soil > soil amended with a high rate of manure. In order to examine the relationship between physical and chemical parameters of media and estrogen mineralization, sewage sludge and biosolid samples with vastly different characteristics were selected for a study of 17 β-estradiol and 17 α-ethinylestradiol mineralization in the presence of ciprofloxacin, an antibiotic commonly used to treat urinary and intestinal infections in humans. Ciprofloxacin was persistent in all media, as less than 0.05% mineralization was observed over 133 d. Despite this persistence, no significant effect of ciprofloxacin addition on 17 β-estradiol or 17 α-ethinylestradiol mineralization was observed at 133 days. Consistent with its chemical structure, maximum mineralization of 17 α-ethinylestradiol was always less than that of 17 β-estradiol, indicating resistance to microbial degradation. PCA analysis indicated that total nitrogen, ammonium-nitrogen and total carbon demonstrated a positive association with respiration and maximum mineralization of 17 β-estradiol, but a negative association with 17 α-ethinylestradiol maximum mineralization. Sorption of 17 α-ethinylestradiol was greater than 17 β-estradiol in all media, limiting maximum mineralization of 17 α-ethinylestradiol.