To investigate the effects of polycyclic aromatic hydrocarbons (PAHs) on the human immune system, analyses were performed on T-cell subsets (CD4(+), CD8(+)), B-cells (CD19(+)), serum immunoglobulin levels (IgG, IgM, IgA) and white blood cell percentages of 16 male workers who were employed in road paving operations and compared to 12 unexposed male controls. PAM exposure was assessed using urinary I-hydroxy-pyrene (1-OHP) levels and was found to be significantly higher in workers than in the controls. While the CD4(+) cell percentage and the CD4(+)/CD8(+) ratio were significantly higher in the PAM-exposed group, the percentages of CD8(+) and CD19(+) cells were unchanged. There was also a significant enhancement in serum IgG levels and the percentage of monocytes in the workers compared to the control group. These data suggest that chronic exposure to PAHs may affect some immune functions in humans. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.