To date, when using the Milwaukee classification for sphincter of Oddi dysfunction (SOD), one cannot accurately classify patients with marginal elevations in laboratory tests; ie, < 1.5 x the upper limit of normal (ULN). Since subsequent treatment may depend on how they are classified, we sought to determine whether these patients should be considered as type II or type III. Between January 1993 and October 1996, 113 consecutive patients (82 females and 31 males; ages 12-87 years) without prior sphincterotomy were referred to consider a diagnosis of SOD type II or III. SOD II patients had pancreaticobiliary-type pain and laboratory elevations >1.5 x ULN or dilated ducts, while SOD III patients had pain only. Hybrid patients had pain and marginal laboratory elevations <1.5 x ULN, with normal duct diameters. Drainage times, frequency, duration, and propagation were not assessed. Sphincter of Oddi manometry (SOM) was performed in each case, and the frequency of abnormal biliary and/or pancreatic basal sphincter pressure was compared, with respect to type II, III, and hybrid SOD. Successful SOM was obtained in 113/114 patients: Abnormal basal sphincter pressure was found in 65, 89, and 43% of type II, hybrid, and type III SOD, respectively. We found no statistical difference between type II and hybrid patients. In contrast, there was statistical difference between types II and III patients and between type III and hybrid patients. In conclusion, there was no significant difference in the frequency of elevated basal sphincter pressure in SOD type II versus hybrid, and thus they should be considered as one group.