p-Nitrophenol (PNP), a toxic nitroaromatic compound, can build up in soils due to extensive usage of nitrophenolic pesticides and hence needs to be removed. Arthrobacter protophormiae RKJ100, a PNP-degrading organism, was used in this work to study factors affecting its growth, and then evaluated for its capacity to degrade PNP in soil microcosms. Molasses (10%) treated with 0.1% potassium hexacyanoferrate was found to be a suitable and cheap carbon source for inoculum preparation. Induction studies showed that PNP depletion was quicker when cells were induced by pre-exposure to PNP. The efficiency of PNP degradation in soil by strain RKJ100 was seen to be dependent on pH, temperature, initial PNP concentration and inoculum size. Microcosm studies performed with varying concentrations (1.4-210 ppm) of PNP-spiked soils showed that strain RKJ100 could effectively degrade PNP over the range 1.4-140 ppm. A cell density of 2x10(8) colony forming units/g soil was found to be suitable for PNP degradation over a temperature range of 20-40 degrees C and at a slightly alkaline pH (7.5). Our results indicate that strain RKJ100 has potential for use in in situ bioremediation of PNP-contaminated sites. This is a model study that could be used for decontamination of sites contaminated also with other compounds.