Six male ayahuasca-experienced volunteers recruited via word of mouth (mean age 32.2) received 3 doses of freeze-dried, encapsulated ayahuasca, measured as 0.5. 0.75 and 1 mg/kg DMT in a pseudo-randomized, single-blind placebo controlled study, with doses administered in ascending order. One participant dropped out after receiving 0.75 mg/kg after a brief but intense experience of disorientation at 0.75 mg/kg DMT. This participant was the least familiar with ayahuasca prior to participation, having reported prior use on only two occasions. Subjective effects were assessed via Spanish-language adaptations of the Hallucinogen Rating Scale (HRS), the Addiction Research Center Inventory (ARCI), and author-designed visual analog scales (VAS) for "liking," "high," "drunken" (dizzy/light headed), "stimulated," "good effect" and "any effect." Side effects were measured through verbal reports and through ARCI "LSD scale" (somatic effects and dysphoria). Heart rate, systolic and diastolic blood pressure (SBP and DBP) were measured every 15 minutes for the first hour and every half-hour for the next four hours. Though SBP and DBP were elevated after all three doses, no dose produced significant differences from placebo, and only a trend for elevated systolic blood pressure was seen at the highest dose (1 mg/kg DMT). Peak changes in SBP occurred at 90 minutes after drug administration and peak DBP changes occurred 60 minutes later. Only 0.75 and 1 mg/kg elevated heart rate, and the elevation was not significant, with an increase from placebo values of 9.2 beats seen after 1 mg/kg and 8 beats seen after 0.75 mg/kg. The lowest dose (0.5 mg/kg DMT) was active in 5 of 6 participants, and produced increases in HRS "somasthenia" (somatic effects), and increases in all VAS scales save "high." All 6 participants distinguished 0.75 and 1 mg/kg from placebo, and these doses increased all VAS scales. The 0.75 and 1 mg/kg doses also increased all HRS scales, including "affect" (changes in emotion), "cognition" (changes in thought), "somasthenia" (changes in bodily sensations or feelings), "perception" (changes in perception) and "intensity." However, neither dose altered "volition" scores (capability of interacting with self and environment). Euphoria and energy (ARCI "MBG" and "A") scales were increased after 0.75 mg/kg, and 1 mg/kg increased dysphoria (ARCI "LSD") in addition to increases in "MBG" and "A" scale. Responses on 5 of 7 VAS scales and HRS "cognition" (changes in thought) scale distinguished 0.75 mg/kg from 1 mg/kg. VAS responses on "drunken," "any effect" and high", and HRS "somasthenia," "affect" and "intensity" distinguished 0.5 mg/kg from 0.75 mg/kg. Side effects included strange somatic sensations, nausea, feeling hot or cold and "electric / tingling feeling." None of the participants in this study vomited. This initial study demonstrated that ayahuasca can be administered safely within a laboratory setting and that it was tolerated in a drug-experienced sample. There is some indication that ayahuasca can produce intense feelings of disorientation in some, but intervention was not required to deal with this experience.