As the marine mussel Mytilus edulis is commonly used as a sentinel species, it would be useful to develop a primary culture of the target organs most often in contact with the marine environment. This study reports an improved method for dissociating the digestive gland and gills of M. edulis and considers the effect of mussel storage on cell viability and functionality before culture initiation. Viability and enzymatic activities such as those of esterase and peroxidase were monitored by flow cytometry, a sensitive, objective technique allowing large volumes of cells to be counted within a short time. A primary culture of digestive gland showed more than 75% viability after 72 h. Mussels were maintained in an aquarium containing clean, oxygenated seawater at 12 °C for two days before culture initiation, and dissociation was performed mechanically and chemically with Ca-Mg-free saline to obtain digestive gland cells. Application of nonspecific esterase activity, using fluorescein diacetate (FDA test) coupled with flow cytometry, characterised the functionality of digestive gland and gill cells in culture.