Extensive culture of stones and of pre-operative and renal pelvic urine for isolation of bacteria and Ureaplasma urealyticum were performed in 70 patients of nephrolithiasis. Stones were subjected to biochemical analysis and scanning electron microscopy. Micro-organisms were isolated from 33 (47%) of 70 renal stones. Of the 38 species of micro-organisms isolated, 14 were urea-splitting (U. urealyticum 2; Klebsiella pneumoniae 8; Morganella morganii 1; Acinetobacter spp 3) and 24 were nonurea splitting. U. urealyticum was cultured from the renal stones of two patients. Pelvic urine, unlike voided urine did reflect the bacteriology of the stone. Biochemically, 55 stones (79%) were calcium oxalate phosphate stones, 10 (14%) were calcium oxalate stones and 5 (7%) were uric acid stones. None of the stones were found to be of struvite composition. These data suggest that infection stones are uncommon in this part of the country. Further, infection of renal stones with fastidious organisms like U. urealyticum and multi-drug resistant bacteria necessitate their removal to ensure complete cure.