The short-term effects of infestation by cowpea aphids (Aphis craccivora Koch) and pea aphids [Acyrthosiphon pisum (Harris)], both Homoptera: Aphididae, on plant growth and respiration of excised, intact shoots of cowpea [Vigna unguiculata (L.) Walp. cv. Caloona], broad bean (Vicia faba L. cv. Aquadulce) and garden pea (Pisum sativum L. cv. Victory Freezer) seedlings were investigated, but not all plant-aphid combinations were utilized. Root, shoot and plant dry weights were significantly reduced within 10 days in the infested plants. Rates of total shoot respiration were significantly greater in infested plants within 10 days, and the increase was not due to increased alternative pathway activity but, rather, to increased cytochrome pathway activity. It is suggested that the aphid-induced increase in shoot respiration may be due to increased rates of photosynthesis, to substances injected into the phloem by the aphids and/or delayed senescence. These data indicate that aphid-infested shoots had a decreased carbon use efficiency.