In vitro tissue culture techniques were employed to study the effects of bacterial endotoxins on the growth of normal epithelial cells from the human ureter (NHU). Primary cultures of NHU cells were initiated from explant outgrowth cultures of human ureteral tissue and cultured on collagen gel in F‐12* medium containing 1% fetal calf serum (FCS). Optimal clonal growth of secondary cultures of NHU cells seeded at relatively low seeding cell densities, directly on plastic dishes, was achieved in F‐12* medium containing bovine pituitary extract (0.5% BPE) and 0.05% BSA. Results indicated that insulin in the F‐12* medium could be replaced by three orders of magnitude less IGF‐1. Further clonal growth experiments demonstrated that PGE1 is growth stimulatory and can replace BPE as a growth factor requirement. This finding was in agreement with the fact that BPE growth requirement could be replaced by cholera toxin or dibutyryl cAMP. These results suggested that both BPE and cholera toxin operated by activation of a cAMP‐dependent mitogenic pathway. Seven gram‐negative bacterial lipopolysaccharides (LPS) and three gram‐positive bacterial lipotechoic acids (LT) were tested for their effects on NHU clonal growth. Three out of the five LPS derived from Escherichia coli (strains 055:B5, 0128:B12, and 0127:B8), LPS from Klebsiella pneumoniae, and LPS from Pseudomonas aeruginosa all showed significant growth inhibitory effects at minimally effective doses ranging from 5 to 25 μg/ml. LPS derived from E. coli strain (0111:B4) had no growth effects at the highest concentration tested (100 μg/ml). In contrast, LT derived from Streptococcus pyogenes, S. faecalis, Staphylococcus aureas, and Bacillus subtilis all markedly enhanced clonal growth at concentrations ranging from 1 μg/ml < [LT] < 50 μg/ml. LT from Strep. pyogenes was inhibitory to clonal growth at 100 μg/ml. The growth inhibitory effects of LPS were shown to be sensitive to the presence of hydrocortisone in the growth medium, indicating that LPS effects on growth are mediated via the arachidonic acid cascade. We speculate that these results indicate a link between the susceptibility of uroepithelial tissue to the pathogenic microflora seen in urinary tract diseases and the differential sensitivity of proliferation‐competent uroepithelial cells to growth inhibition by LPS produced by gram‐negative bacteria. However, further studies with uropathogenic serotypes will be necessary to corroborate this possibility. The growth‐stimulating activity of LTs produced by gram‐positive bacteria may be due to their ability to bind to cell‐associated fibronectin and to activate the fibronectin receptor as part of ligand receptor–induced mitogenic transmembrane signalling pathway. Copyright © 1992 Wiley‐Liss, Inc.