The presence of massive deciduomata prolongs pseudopregnancy in the rat until about the normal time of parturition. This prolongation is related quantitatively to the amt. of decidual tissue present. Ovulation and vaginal cornification are suppressed while it is apparent that the functional life of the corpora lutea is extended. Hysterectomy or simple laparotomy is without effect upon the normal duration of psuedopregnancy.