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Primary cultures of muscle tissue from 10-day-old embryos of Locusta migratoria and 11-day-old embryos of Schistocerca gregaria have been grown and maintained in 5+4 insect medium and Grace's insect medium. Myofibres grown in 5+4 medium reached maximum size after about 5 weeks in culture and could be maintained for 2–3 months. They were often branched and rarely striated in appearance. Those rown in Grace's medium reached maximum size within 3 weeks and could be aintained for about 4 weeks in toto. They were striated and resembled, at least superficially, locust myofibres in vivo. Patch-clamp recordings from myofibre cultures grown in 5+4 medium, either on the myofibres or from excised membrane patches, indicated the presence of a diffusely-distributed population of receptors for L-glutamate. 10−6 moll−1 concanavalin A blocked the desensitization of these receptors. The glutamate receptors gated large conductance channels which had reversal potentials of about 0mV. The amplitude of the channel current was sensitive to the concentration of calcium in the membrane environments.