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Data on the sugar compositions of floral nectars were used to test the hypothesis that the Hawaiian Lobelioideae (Campanulaceae) were pollinated by nectarivorous passerine birds (Fringillidae subfam. Drepanidinae, Meliphagidae) prior to widespread extinctions among the native avifauna. Nectars from 24 individuals (representing different taxa [three genera, ten species, and three interspecific hybrids], different conspecific populations, and different individuals within a population) were analyzed via high‐performance liquid chromatography (HPLC). Mean percentages (±one S.D.) and ranges (parenthetically) for each sugar were: fructose, 43.5 ± 2.8% (37.2%–48.3%); glucose, 54.5 ± 3.1% (47.2%–62.8%); and sucrose, 2.0 ± 1.6% (0.0%–5.3%). These nectars are thus hexose‐dominant (mean sucrose‐hexose ratio of 0.019 ± 0.017), the type preferred by passerine birds.