AIM: To investigate whether Helicobacter species (Helicobacter spp.) could be detected in hepatocellular carcinoma (HCC) tissue.METHODS: Liver samples from 28 patients with hepatocellular carcinoma (HCC) diagnosed by histopathology were studied. Twenty-two patients with other liver diseases (5 with liver trauma, 7 with cavous liver hemangioma, 6 with liver cyst and 4 with hepatolithiasis), 25 patients with gastric cancer, 15 with colonic cancer and 15 with myoma of uterus served as controls. Two piceces of biopsy were obtained from each patient. One was cultured for Helicobacter spp. and extraction of DNA, the other was prepared for scanning electron microscopy (SEM) and in situ hybridization. The samples were cultured on Columbia agar plates with microaerobic techniques. Helicobacter spp. in biopsy from the studied subjects was detected by polymerase chain reaction (PCR) with Helicobacter spp. 16S rRNA primers. Amplified products were identified by South hybridization and sequenced further. Besides, other genes (vacA, cagA) specific for Helicobacter pylori (H pylori) were also detected by PCR. Helicobacter spp. in biopsies was observed by SEM. Transmission electron microscopy (TEM) was performed to identify the cultured positive Helicobacter spp. The presence of Helicobacter spp. was detected by in situ hybridization to confirm the type of Helicobacter.RESULTS: The positive rate of Helicobacter cultured in HCC and gastric cancer tissue was 10.7% (3/28) and 24%(6/25), respectively. Helicobacter microorganisms were identified further by typical appearance on Gram staining, positive urease test and characteristic colony morphology on TEM. The bacterium was observed in adjacent hepatocytes of the two HCC samples by SEM.The number of cocci was greater than that of bacilli. The bacterium was also found in four gastric cancer samples.PCR showed that the positive rate of HCC and gastric cancer samples was 60.7% and 72% respectively, while the controls were negative (P＜0.01). The PCR-amplified products were identified by South hybridization and sequenced. The homology to 16S rRNA of Hpylori was 97.80%. The samples were verified byin situ hybridization for Helicobacter spp. 16S rRNA-mRNA and proved to be H pylori positive. There was no statistical significance between HCC and gastric cancer (P＞0.05), but the positive rate of HCC and controls had statistical significance (P＜0.01). Only 3 HCC samples and 2 gastric cancer samples of the cagA genes were detected. None of the samples reacted with primers for vacA in the two groups.As for the genotype of H pylori, type Ⅱ had preference over type Ⅰ.CONCLUSION: Helicobacter infection exists in liver tissues of HCC patients. Helicobacter spp. infection is related with HCC, which needs further research.