Flow cytometric (FCM) immunophenotyping has an important role in the diagnostic work up of fine-needle aspiration (FNA) specimens obtained from lymphoid lesions. The objective of the present study was to evaluate the feasibility of this method with respect to referred FNA specimens. One hundred and two FNA specimens referred to our laboratory for FCM analysis during the last 3 years were studied. Specimens were sent, accompanied by cytological smears, from 11 distant hospitals by ordinary mail. The evaluation of potential B-cell monoclonality, the main diagnostic issue to be resolved using FCM, was possible in 86 of these 102 cases. The remaining 16 samples could not be analyzed or adequately interpreted because of sparse or necrotic material. A monoclonal B-cell population was found in 17/86 satisfactory cases, of which 16 were histologically confirmed. Eight cases contained cells positive for the epithelial marker Ber-EP4 and were diagnosed accordingly as carcinomas. FCM analysis of specimens obtained with a clinical question of Hodgkin lymphoma or T-cell lymphomas did not yield definitive data. The time lapse between sampling and analysis (12-84 hr) did not affect the results. This probably was due to the fact that all aspirates were taken in Roswell Park Memorial Institute (RPMI) cell medium, supplemented with 50% fetal calf serum. In conclusion, this retrospective study establishes that it is possible, in the majority of cases, to refer FNA material for FCM immunophenotyping by mail, and that results regarding B-cell clonality in the case of small-cell lymphomas are reliable also after a transportation period of 3-4 days. Carcinoma may be similarly diagnosed and a diagnosis of lymphoma may be excluded in reactive proliferations. Cases with only a few atypical cells or specimens from patients suspected of having Hodgkin lymphoma or T-cell lymphomas are not suitable for analysis by FCM.