Lymphocyte subsets and prenatal exposure to the PCB congeners CB-28, CB-52 and CB-101. Unadjusted means (± SE) of numbers and percentages of lymphocyte subsets in three months old infants prenatally exposed to the sum of CB-28, CB-52 and CB-101. Lipid-adjusted serum concentrations of the PCB compounds in the blood of the mothers in late pregnancy (week 32–34) were used as a measure of prenatal exposure. Infants having an infection within a 7 day period before sampling were excluded from the statistical analyses. The exposure variable was categorized since over 40% of the mothers had serum lipid levels of the PCBs below the limit of quantification (reference category 1). An effort was made to have equal numbers of participants in the two other exposure categories. *Significantly different from the group with the lowest exposure (reference category 1) (N = 45–50, p ≤ 0.01).