This study reports the validation of an automatic assay for milk triglycerides, as well as the association between milk xenobiotic concentrations and milk triglycerides. The correlation between this assay and a gravimetric reference method for total fat was good (r = 0.997). Triglycerides and xenobiotics were measured in breast milk sampled from one mother. She received two water-soluble drugs, tetracycline and doxycycline in two courses. The levels of organochlorines (DDE, PCB) were also measured and related to those of fat in milk samples from this mother. These and previous results indicate that milk triglyceride variations influence the concentrations of lipophilic xenobiotics in milk.