The biological control of Meloidogyne arenaria on peanut (Arachis hypogaea) by Pasteuria penetrans was evaluated using a six x six factorial experiment in field microplots over 2 years. The main factors were six inoculum levels of second-stage juveniles (J2) of M. arenaria race 1 (0, 40, 200, 1,000, 5,000, and 25,000 J2/microplot, except that the highest level was 20,000 J2/microplot in 1995) and six infestation levels of P. penetrans as percentages of J2 with endospores attached (0, 20, 40, 60, 80, and 100%). The results were similar in 1994 and 1995. Numbers of eggs per root system, J2 per 100 cm(3) soil at harvest, root galls, and pod galls increased with increasing nematode inoculum levels and decreased with increasing P. penetrans infestation levels (P 0.05). There were no statistical interaction effects between the inoculum levels of J2 and the infestation levels of P. penetrans (P > 0.05). When the infestation level was increased by 10%, the number of eggs per root system, root galls, and pod galls decreased 7.8% to 9.4%, 7.0% to 8.5%, and 8.0% to 8.7% in 1994 and 1995, respectively, whereas J2 per 100 cm(3) soil decreased 8.8% in 1995 (P