Organ-specific lung and liver metastatic variants of the murine TA3/Ha mammary adenocarcinoma cell line were selected by sequential in vivo growth with intervening in vitro cell culture. These variants readily formed specific lung or liver metastatic lesions upon i.v. injection into A/J mice. TA3/Ha cells produce a large cell surface glycoprotein called epiglycanin, which contains a high proportion of Thomsen-Friedenreich (TF) antigenic structures. The presence of non-cryptic TF has been associated with malignancy in humans and animals. We used peanut lectin agglutinin (PNA), which has a preferential affinity for TF antigenic structures, to determine whether these selected metastatic variants retained the TF antigen expression. In vitro, the TA3/Ha metastatic variant lines exhibited strong PNA binding similar to that seen with human RBC after neuraminidase treatment to expose the cryptic TF antigen. In contrast, the non-epiglycanin-producing TA3/St subline did not bind PNA appreciably. Autoradiography of liver sections with TA3/Ha metastatic lesions after 125I-PNA i.v. indicated an avid uptake throughout the viable tumor mass and FITC-PNA staining of these tissue sections readily identified the metastatic tumors under fluorescence microscopy. Tissue biodistribution studies revealed that lung or liver containing the TA3/Ha metastatic variant nodules retained about 7 to 8 times as much of an i.v. dose of radioiodinated PNA as did controls, allowing for clear delineation of tumor-infiltrated lung or liver by gamma scintigraphy. These in vitro and in vivo tests confirm that the selected organ-specific TA3/Ha variants retained the binding characteristics of the parent TA3/Ha line. These observations illustrate the potential utility of radiolabelled PNA for the detection of TF-antigen-expressing tumors and metastases. This murine system with organ-specific TA3/Ha metastatic variants also provides a model for evaluation of various other macromolecular probes for tumor radioimmunodetection of metastatic lesions.