The development of non‐toxic or non‐polluting antifouling additives that can be formulated in practical coatings requires assays involving target organisms. Assays that test both for the effective and toxic concentrations of active compounds are useful. It is also desirable if the assay can provide information regarding the performance that can be expected if the compounds are incorporated into different matrices. Described here are the simple laboratory assays that have been developed using the barnacle,Balanus amphitrite, a common fouling organism found throughout temperate and tropical seas. One of the assays depends on synchronous year‐round mass culture, the procedure for which is described, of cypris larvae. The laboratory assays provide quantitative estimates of toxicity and settlement inhibition of barnacles. The methods described provide an excellent system for the use of barnacles to study the interaction of the test compounds and surfaces.