Joint effects of dioxin related chemicals (DXNs), hexachlorocyclohexanes (HCHs), DDT, dieldrin, heptachlorepoxide (HCE), chlordane and polychlorinated biphenyls (PCB) on the levels of triirodothyronine (T3), thyroxine (T4), thyroid stimulating hormones (TSH) and thyroid binding globulin (TBG) in the peripheral blood of 101 breast-fed infants are studied. The statistical issue involved is how to estimate the effects based on data from volunteer subjects with possible measurement errors. A chain independent graph is applied for modeling the associations among factors, and dicotomizations of selected factors are performed for estimating the effects. Use of nonparametric methods with careful consideration of over-adjustment is suggested. It is shown that the estimated odds ratios of DXNsboolean ORDDT, the first principal component of DXNs and DDT, relative to TSH are 3.02 (p-value = 0.03) and 7.15 (p-value = 0.02), respectively, when PCB is not adjusted and adjusted for, respectively. Copyright (C) 2003 John Wiley Sons, Ltd.