The bilaids are tetrapeptides with an unusual alternating LDLD chirality isolated from an Australian estuarine isolate of Penicillium sp.. Bilaids are weak μ-opioid agonists (Ki = 3.1 µM using HEK293 cell membranes expressing the human receptor) that inhibit forskolin-induced cAMP accumulation in HEK293 cells expressing the human µ-opioid receptor by 21% when used at a concentration of 10 µM.