This paper describes the in situ presence and distribution of collagen types I, III, IV and V in the bovine placenta. The objective was to determine whether there are qualitative and/or quantitative differences in the collagen content of placentomes originating from cows with retained placenta and cows with normal discharge of placenta. Twelve h post partum discharge of the placenta or the incidence of retained placenta was monitored. From 57 cows one placentome per cow was collected within 1 h post partum. The cows were divided into three groups: retained placenta after caesarean section (Group 1), retained placenta after spontaneous calving (Group 2) and normal discharge of placenta within 12 h post partum after spontaneous calving (Group 3). A pilot study was conducted to establish the technique of collecting the placentomes and to verify the applied immunohistological methods used in this work. In the following study, 32 placentomes were used to determine the amount of collagen (types I, III, IV and V) with qualitative and semi-quantitative methods using immunohistochemical techniques. Collagen types I, III, IV and V were found in large quantities in the maternal tissue. In the fetal connective tissue the amount of these collagen types was smaller. In the placentomes of the three groups, no qualitative or quantitative differences could be detected.