Warm‐water species of siphonophores, medusae, ctenophores, heteropods, pseudothecosomatous pteropods, salps, and doliolids were individually collected in jars by SCUBA divers in the western North Atlantic Ocean. In situ rates of oxygen consumption and ammonium excretion were estimated by difference from control jars of seawater enclosed simultaneously. The cystonect siphonophores Rhizophysa filiformis and Bathyphysa sibogae had low respiration and excretion rates [4–7 µl O2 (mg protein‐h)−1 and 0.3–0.5 NH4+(mg protein‐h)−1], while several calycophore siphonophores, heteropods, and salps had high rates [19–192 µl O2 (mg protein‐h)−1 and 1.0–3.1 µg NH4+ (mg protein‐h)−1]. Most O: NH4+ ratios ranged from 16–38 and suggest that both protein and lipid are important metabolites in tropical and subtropical gelatinous zooplankton. Many physonect siphonophores, scyphomedusae, heteropods, and salps excreted ammonium at rates exceeding 0.3 µg‐atom NH4+‐N h−1 and may play an important role in recycling nitrogen in the upper mixed layer of oligotrophic ocean regions.