This article reports on a rapid assessment (RA) carried out in the city port of Mombasa, Kenya in March 2004 by the Omari Project to inform the scaling up of their services to heroin users. Heroin has been a street drug in Mombasa for over 25 years. From 1998, white crest, probably from Thailand, started to replace brown sugar, and there was a major shift from inhalation of the vapor ("chasing the dragon") to injecting. The Omari Project has been monitoring the heroin situation in Mombasa and treating heroin users from Mombasa since 1997. In the course of the RA, 496 heroin users were interviewed of whom 95% were men and 5% were women. A range of methods were used, including mapping of the Mombasa region, work with a key informant/guide who was a heroin user, administration of a brief questionnaire and informal interviews, and feedback of findings to other local agencies working with drug users. Respondents were from a wide range of cultural/ethnic groups, the two largest being Mijikenda and Swahili, who are indigenous to the Kenya coast. Overall, 15% of respondents had "ever injected" heroin, and 7% were current injectors (n = 37). These data indicate a shift away from injecting but also reflect the death of many established injectors, either through overdose or AIDS or hepatitis. The figure of 7% of the sample reporting being current injectors is likely to be an underestimate. Syringes were available from a number of pharmacies and most injectors reported using a syringe for 1-3 days. The majority reported injecting in a group of three or more and described risk behaviors for HIV transmission. The results of the assessment highlight the need for a range of services, including needle exchange, counseling, and referral to residential treatment programs. However, progress toward responding to the findings of the RA by establishing effective services are hampered because of legal impediments to operating needle exchange programs in Kenya.