This study was an attempt to identify if there are any trends in excretion of 1,2,3,4,5,6-hexachlorocyclohexane (HCH) isomers alpha-, beta-, and gamma-, hexachlorobenzene (HCB), [1,1,1-trichloro-2, 2-bis(4-chlorophenyl)ethane] (p,p'-DDT), [1,1-dichloro-2, 2-bis(4-chlorophenyl)ethane] (p,p'-DDD), [1,1-dichloro-2, 2-bis(4-chlorophenyl)ethylene] (p,p'-DDE), and polychlorinated biphenyls (PCBs) with human milk during lactation. The shortest lactation studied took 16 weeks, and the longest 84 weeks. Three hundred fifty-two milk samples, collected from each donor once a week, were examined. The analysis of the result showed individual differences in the excretion of the compounds. The findings from this study are not conclusive enough to claim that there are consistent trends showing a decrease or increase in the excretion of the compounds under examination. Thus, one cannot claim that the infants' exposure to those compounds decreases or increases as breast-feeding continues.