Chromosome 17q is highly susceptible to rearrangement mutations in breast cancer. c-erbB-2 at 17q11.2 approximately q21.1 is frequently amplified, as is a region at 17q22 approximately q24. As a step in the search for the target gene(s) of the 17q22-q24 amplification we determined whether the placental lactogen (PL) genes at 17q23 were amplified in 59 breast carcinomas. These genes were selected as their upregulation could theoretically be involved in breast cancer tumorigenesis. Amplification of the PL genes, and also of c-erbB-2, was detected using semi-quantitative PCR. The reliability of this method was confirmed since c-erbB-2 results obtained using PCR, Southern blotting and immunohistochemistry were in good agreement. The PL genes were amplified in 13 (22%) of the tumors. Furthermore, the PL and c-erbB-2 genes were frequently co-amplified although there is a non-amplified region between them. Expression of PL was investigated in 26 tumors and was detected in 16 of these cases including all 10 tumors with amplification of the PL genes. The tumors with PL gene amplification were all aneuploid. A trend was seen towards an increased incidence of lymph node involvement for tumors with amplification of the PL genes and for tumors with co-amplification of PL and c-erbB-2, which suggests a possible association with high malignancy.