BACKGROUND: Intraductal ultrasonography (IDUS) using thin ultrasonic probes could be useful in some biliopancreatic indications. Initial prototypes were limited by the size of the probes and their fragility. Insertion was then mainly performed via a transhepatic route. Two new thinner Olympus miniprobes could allow performing IDUS routinely via ERCP. AIM: To evaluate the technical features of these miniprobes. METHODS: UM-S20-20R (SP) with a tip of 1.7 mm and UM G20-29R (SG) with a channel for a 0.035 inches guidewire (tip=2.0 mm) have a 20 MHz frequency. Insertion can be done transpapillary (via ERCP) or percutaneously (via transhepatic route). Limiting factors for the probe insertion and the image quality were studied. RESULTS: 30 intraductal biliary EUS were performed in 25 patients (staging and/or follow-up of ampulla or bile duct tumors: 18; indeterminate biliary stenosis: 8; mucinous producing pancreatic tumor (MPPT): 4). - In 3 cases (Klatskin's tumors) SP was inserted after a percutaneous drainage inside a 12 F catheter, without technical problems; the image quality was not affected by the drain, and the interface was excellent. - In 27 cases a transpapillary insertion was intended. SP was used in 7 cases. Insertion succeeded in 3 sphincterotomized patients but only in 1/4 non sphincterotomized patients. The insertion through a biliary stenosis failed 2/3. SG was used in 20 cases. It was inserted in biliary ducts in 16/16 patients. A precut was once necessary. The insertion inside the wirsung until the tail was performed 4/4 without problem. SG passed through biliary stenosis 13/15. In two Klatskin's tumors one hepatic duct was not catheterized by the guidewire. Two factors hampered the interpretation: - air artifacts (after sphincterotomy and in MPPT) – large tumors (limited penetration depth). No probe rupture was observed. CONCLUSION: 1. The slim probe is a good option for transhepatic route due to its size allowing a smaller diameter for the drainage catheter 2. The miniprobe with guidewire is better for the transpapillary route avoiding sphincterotomy and overcoming stenotic areas. It could now be used routinely during ERCP.