The ovary of the lobster, Homarus americanus, is encased by a nonstriated muscular wall that is thought to contract and extrude the oocytes at spawning. The cells of this lobster ovarian muscle (LOM) are unconventional in that their contractile apparati contain extensive arrays of microtubules in addition to actin and myosin. In this study, we introduce two assays to measure LOM contraction in vitro. One assay ranks the distinct morphological changes that a contracting LOM muscle strip progresses through to quantify the extent of contraction. In the other assay, the distances that the edges of LOM strips travel during contraction are measured from a video monitor to calculate a rate of contraction. Using these assays, we found that compounds that elevate intracellular cAMP (IBMX, forskolin, and dbcAMP) inhibit LOM contraction. The biogenic amines octopamine (OCT), 5-hydroxytryptamine (5-HT), and dopamine (DA) were tested for their ability to stimulate LOM contraction in vitro. Octopamine (10−6–10−4 M) significantly stimulates contraction in a dose-dependent manner, and 5-HT (10−5–10−3 M) mildly stimulates contraction. Dopamine has no effect on contraction. The opposing effects of forskolin and OCT on LOM contraction indicate that OCT stimulation is not mediated through class two OCT receptors. Therefore, LOM appears to be controlled by either class one OCT receptors or a novel class of OCT receptors. © 1992 Wiley-Liss, Inc.