In this study, we have investigated the effect of hydrophobic and hydrophilic unconjugated bile acids (UBAs)-ursodeoxycholic acid (UDCA), chenodeoxycholic acid (CDCA), lithocholic acid, and colic acid-on chemotaxis in adult and neonatal human polymorphonuclear leukocytes (PMNs). The trypan blue exclusion dye test was preliminarily performed to determine the toxicity of the studied UBAs on PMNs. N-formyl-methionyl-leucyl-phenylalanine (100 nM) was used as a chemoattractant. Chemotaxis (1 x 10(6)cells/mL) was analyzed in the presence or absence of UBAs (10 microM) by blind well chambers. The antioxidants vitamin E and vitamin C were tested for their ability to reduce the inhibitory effect of UBAs. We found that only CDCA was able to induce damage in PMNs in the range of 1-40 microM. Both CDCA and UDCA were able to inhibit chemotaxis in PMNs, whereas lithocholic acid and colic acid were ineffective. The inhibitory effect was reversible inasmuch as PMNs incubated with either CDCA or UDCA and subsequently washed showed normal chemotaxis. Concomitant incubation of PMNs with UBAs and vitamins C or E reversed the inhibition. We did not find substantial differences between PMNs from adults or newborns. In conclusion, CDCA and UDCA are able to reduce, in a specific and reversible fashion, both adult and newborn neutrophil chemotaxis. As concomitant incubation of UBAs and electron scavengers restores PMN chemotaxis to control values, we conclude that free radicals may be involved in the mechanism of inhibition. We speculate that this defect may contribute to the impaired host response described in cholestatic patient.