Three cDNAs encoding members of the pregnancy-specific beta 1-glycoprotein (PSG) family were isolated from human term placental cDNA library. All three cDNAs encode proteins with similar domain structure. There is a leader sequence of 34 amino acids followed by an N-domain of 109 amino acids. Immediately after the N-domain are one or two copies of a repeating A-domain of 93 amino acids, a B-domain of 85 amino acids and a C-domain of variable size. The proteins are highly hydrophilic. However, one of them has an 81-amino acid C-domain which is very hydrophobic and could potentially serve as a membrane attachment site. The putative cell-cell recognition tripeptide, Arg-Gly-Asp, is present in the N-domain of two of the proteins. Partial sequence of one of the cDNAs has been found in HeLa cells while cDNAs highly homologous to two of the cDNAs have been found in the fetal liver. Functional roles of the PSG proteins basing on their structure are proposed.