Chiasma frequency and chiasma distribution pattern of three parasite flukes, Schistosoma mansoni (n=8), S. japonicum (n=8), and Paragonimus ohirai (n=11) were investigated by using the chiasma distribution graph. It was revealed that there is a minimum value of interference distance between two interstitial chiasmata in each bivalent (1.8% of the total bivalent length), but frequency distributions of interstitial chiasmata are random and almost uniform except the centromere and telomere regions in which chiasma formation is suppressed. As no chiasma terminalization was detected, the so-called terminal chiasma were best interpreted by an achiasmatic terminal association resulting from the telomerenuclear membrane association. The mean chiasma frequency per cell estimated from interstitial chiasmata is 15.3 in S. mansoni and P. ohirai, but very low (3.0) in S. japonicum. A genetic mechanism controlling the level of chiasma frequency was discussed with reference to the results in mammals.