1. Radiolabeled peptides released from an isolated cluster of bag cell neurons, during an after discharge, were compared with the polypeptide egg-laying hormone (ELH), 4,500 daltons, pI 9.0-9.3, as purified from homogenates of bag cell clusters. A peptide, labeled with methionine, leucine, and arginine, which is selectively released from after discharging bag cell clusters comigrates with marker ELH, purified from cluster homogenates, on P-6 gel filtration columns and subsequent isoelectric focusing gels. At least three other presumed peptides of unknown function are also released, including one of 5,000-6,000 mol wt, pI 4.5-5.0. 2. When bag cells afterdischarge in vitro, bioactive material is released that will induce egg laying when injected into an Aplysia. This released bioactive material also comigrates with bioactive material from cluster homogenates on P-6 columns. 3. These experiments demonstrate that ELH (4,500 mol wt, pI 9.0-9.3), as purified from bag cell cluster homogenates, is also the major form secreted from bag cells that induces egg laying. This purified ELH can now be used to study the physiological effects of a secreted neurohormone and their relationship to behavior.