Field studies were conducted for 15 species of Iochroma Benth. and the nested genus Acnistus Schott to quantify the diversity of pollination systems and to assess the potential contribution of pollinator behavior to the persistence of closely related species in sympatry. We combined measures of pollinator visitation and pollen deposition to estimate the importance of major groups of pollinators for each species, and we calculated proportional similarity in the pollinator assemblage among species. We found that 12 species of Iochroma, encompassing a range of flower colors and sizes, were principally pollinated by hummingbirds and, in many cases, by the same hummingbird species. The remaining species were either pollinated by a mix of hummingbirds and insects (two species) or exclusively by insects (two species). Based on proportional similarity values, the overlap in pollinator assemblages was found to be higher for sympatric species than for allopatric ones, reflecting sharing of local pollinator fauna. However, observations of individual pollinator fidelity, perhaps related to territorial interactions among hummingbirds, suggested that pollinators may still contribute to the reproductive isolation of sympatric congeners. Nonetheless, because interspecific pollen flow does occur, the maintenance of species boundaries in sympatry probably requires postmating reproductive isolating mechanisms.