To investigate the potential for differential accumulation of paralytic shellfish toxins (PSTs) in various tissues of the akoya pearl oyster, Pinctada imbricata, two feeding trials were carried out using the PST-producing dinoflagellate, Alexandrium minutum. When fed with A. minutum at concentrations between 100 and 1300 cells ml(-1), the maximum clearance by P. imbricata was shown to occur at a density of 300 cells ml(-1). When fed twice daily at this rate for up 12 days, P. imbricata accumulated analogues of gonyautoxins (GTXs): GTXs 1,4 and 2,3. The levels of GTXs in the viscera increased progressively on days 4, 8 and 12 to peak at 17.9+/-4.47 microg STX-equivalent 100 g(-1) biomass. Following 12 days of depuration, in the absence of A. minutum, GTX levels fell by approximately 65% to 6.0+/-2.20 microg STX-equivalent 100 g(-1) biomass. No GTX was found in the oysters at the start of the trial or in untreated controls. The accumulation of GTX was found to be tissue specific. No GTX was detected in the muscle tissue of P. imbricata during the feeding trial.