Morphology of sperm phagocytosing rat peritoneal macrophages (PM) in control and Lipiodol added cultures was evaluated under light as well as scanning electron and transmission electron microscopes. The spermiophagic index (SPI) was assessed to estimate an inhibitory effect of Lipiodol on sperm phagocytosis to be compared with the outcome of morphological studies. Lipiodol inhibits in vitro sperm phagocytosis as indicated by SPI and evaluation under light, scanning electron and transmission electron microscopes. The highest SPI was seen in control cultures (14.44), declined in cultures with 0.25% and 0.5% Lipiodol (3.3 and 3.02 respectively) to reach the lowest value with 1% Lipiodol (1.60). The macrophages in cultures with Lipiodol were covered by a thin layer of oily contrast medium. The layer produced changes in the macrophages' shape and the cytoplasmic surface configuration. Lipiodol hinders both sperm phagocytosis and movement of PM by altering their shape and impairing pseudopodia and protrusions formation. Morphological studies of sperm phagocytosis by PM can help explain therapeutic effects of oily contrast media used in hysterosalpingography. Number of studies have suggested therapeutic effects of hysterosalpingography (HSG). These studies have demonstrated an increase in pregnancy rates after HSG in previously infertile women (Fullenlove, 1969; Palmer, 1960). Pregnancies were even more numerous after applying oil, than water based contrast media (DeCharney et al., 1980; Schwabe, 1983). Sawatari et al., 1993 have lately shown, that Lipiodol significantly increases pregnancy rates in animals. Hypothesis has been put forward as to the possibility of modulating activity of these agents exerted upon the peritoneal and oviductal macrophages (Boyer et al., 1986; Schwabe et al., 1983).(ABSTRACT TRUNCATED AT 250 WORDS)