Pichia anomala 2.2540, isolated from soil contaminated by crude oil, degraded naphthalene, dibenzothiophene, phenanthrene and chrysene, both singly and in combination. The yeast degraded 4.5 mg naphthalene l(-1) within 24 h. Phenanthrene was degraded after a lag of 24 h. When a mixture of all four polycyclic aromatic hydrocarbons was treated at either 0.1-1.6 mg l(-1) or 3.1-5.3 mg l(-1), naphthalene was completely degraded first within 24 h, followed by phenanthrene and dibenzothiophene after 48 h. Chrysene, which remained in the mixture even after 96 h, could be degraded along with naphthalene. Chrysene at 0.7 and 1 mg l(-1), in the presence of 4.3 and 65 mg naphthalene l(-1), respectively, was removed within 96 h.