Four bacterial strains isolated from a mangrove swamp oilfield location in the Niger Delta of Nigeria were cultured aerobically in the presence of 1.0% waste drilling fluid to determine the effect of the waste on their growth. A 2-h lag phase of growth was produced by the waste in cultures of Micrococcus and Pseudomonas species, while the waste increased the lag phases of Alcaligenes and Staphylococcus species to 4 h. The exponential phase of growth of Pseudomonas sp. was depressed by the waste drilling fluid but fluid stimulated the exponential phases of Micrococcus and Alcaligenes spp There was enhancement of the growth rare of Alcaligenes and Micrococcus spp. while those of Staphylococcus and Pseudomonas spp. were decreased. The depressed growth rates of Staphylococcus and Pseudomonas spp. in the presence of the waste drilling fluid might lead to a decrease in their contribution to the removal of the waste from the environment during spillage or disposal and, therefore, may result in an accumulation of the waste in the environment. (C) 1996 Elsevier Science Ltd.