Ethanol decreases synaptic transmission at the neuromuscular junction of the Superficial Flexor Muscle (SFM) system of the crayfish in a dosage-dependent manner (Jensen et.al., Program # 465.15, 2002 Abstract Viewer, SFN, 2002. CD-ROM). We continue studying the effects of ethanol on the SFM system of Procambarus clarkii by exposing the system to 2% ethanol under Ringers of varying calcium concentrations. Stable junction potentials (JPs) were recorded with microelectrodes while stimulating axon 6. The solution bathing the preparation was changed to one containing 2% ethanol in normal (100%), low (30%) or high (200%) calcium Ringers, and JP sizes were recorded every 3 min. for up to 18 min. before removing the drug. In experiments using normal Ringers before drug exposure, JPs decrease to 50% of their former size within 3 min. upon exposure to 2% ethanol in normal Ringers, and remain stable thereafter. They decline to less than 40% of their former value if they are exposed instead to 2% ethanol in either 30%...