A portion of peritonitis episodes are reported as culture-negative or as initial no growth peritonitis (INGP). To determine if demographics, symptoms, signs, treatment, and outcome were different in INGP when compared to culture-positive peritonitis (Pos), we examined data from the Network 9 Peritonitis and Catheter Survival Study. Only peritonitis episodes occurring in adults with peritoneal dialysis (PD) fluid WBC counts greater than 100 were included in the analysis. INGP accounted for 14% of the episodes of peritonitis. Organisms grew out of 13 of the 37 patients in INGP that were recultured: 3 fungal, 5 gram-negative, and 5 gram-positive isolates. A difference in culture methodology for the two groups could not be detected. There was no difference in gender, race, incidence of diabetes, previous peritonitis, or exit-site infections between the two groups. INGP had a greater percentage of patients over age 70 (23.3% vs 14.7%, p < 0.05), and a larger percentage of INGP patients placed additives in their dialysate (55% vs 43.6%, p < 0.05). There was no difference in symptoms or signs between the two groups. The INGP group had half the catheter removal rate (9/103 vs 110/630 for Pos, p < 0.05), otherwise, there was no difference in the rate of hospitalization, death, or switch to hemodialysis. There was no difference in types of drugs used or method of drug administration between the two groups. A lower percentage of INGP patients were treated for 6 days or less and a higher percentage received 7-10 days of intraperitoneal (IP) therapy when compared to Pos.(ABSTRACT TRUNCATED AT 250 WORDS)