One possible strategy to tackle the negative effects of urban freight is the substitution of cars by electric cargo bikes for inner-city courier shipments. This paper determines whether there is a potential market for electric cargo bikes, how the current market is organized, how electric cargo bikes are perceived by bike and car messengers, and what factors drive their willingness to use them. We find that in terms of cost, payload and range, electric cargo bikes lie in between two existing modes (bikes and cars) that have a largely overlapping market. Vehicle choice is commonly made by freelance messengers, as many courier companies don't operate their own fleets. Therefore they can contribute only indirectly to the dissemination of electric cargo bikes by considering them in their operational management. Despite the fact that most messengers have not used an electric cargo bike before, it was generally regarded to be suitable for courier shipments. Using a binary logit model, we find that messengers' demographics, their professional practice as well as their attitudes and values have significant impacts on their willingness to use electric cargo bikes. Critical factors for actual implementation appear to be electric range, purchase price and publically available information.