 This is a randomized, open-label study designed to assess the safety and efficacy of AQUAVAN Injection versus midazolam HCl following pretreatment with an analgesic, fentanyl citrate injection, in producing sedation in patients undergoing colonoscopy. Randomization will be stratified by site. Following completion of pre-procedure sedation assessments, patients will be randomly assigned to 1 of the 2 i.v. treatment groups at a 3:1 AQUAVAN Injection: midazolam HCl allocation ratio. All study patients, irrespective of treatment group assignment, will receive fentanyl citrate injection as an analgesic pretreatment. Supplemental doses of fentanyl citrate injection may be administered if the patient reports pain or if inadequate analgesia is present as demonstrated by increased heart rate andor blood pressure in the presence of adequate sedation. At no time should fentanyl citrate injection be administered to increase sedation levels. AQUAVAN Injection and midazolam HCl will be administered to induce a state of adequate sedation, defined as a Modified Observers Assessment of Alertness Sedation OAAS score of 4 or less. Supplemental doses will be administered to increase depth or duration of sedation. Supplemental doses will not be administered if the Modified OAAS score is 2 or less or if there is no purposeful response to stimulation. The depth of sedation will be measured by the Modified OAAS scale, a validated measure. Patient and Investigator assessments will be used to confirm the depth of sedation provided met the goals of sedation, reduction of anxiet, and reduced awareness. 