Our systematic studies of different types of benign and malignant salivary neoplasms in humans were initiated about two years ago. Analysis of karyotypes revealed that virtually all tumors are associated with chromosomal abnormalities. That those abnormalities may also take part in tumor initiation and progression is suggested by the association of specific chromosome rearrangement with particular cancers. We here with report cytogenetical observation in five Warthin's tumors giving particular attention to the possible occurrence of cells with (a) a normal karyotype or with (b) numerical changes, either loss of the Y chromosome or monosomy 4. The present series od adenolymphomas was karyotyped by a direct chromosomal analysis method. The method reported was highly successful, in several types of tumors showing the possibility of having good banded metaphases. All Warthin's tumors showed stemline (S) with a normal karyotype. These normal cells constituted the only S in two cases and the primary S in the other three cases. The normal cells observed in all adenolymphomas could be interpreted as outgrowing stroma cells. Most types of previously well-studied benign human tumor types, however (meningiomas, pleomorphic adenomas, lipomas), has a S group with a normal karyotype, regardless of the the tissue culture technique used. Thus, we believe that these normal cells usually represent neoplastic elements. Furthermore, we think that all benign tumors originate with a rather normal S, which, however, as the first indication of neoplastic transformation, shows chromosomal instability, such as the loss of chromosomes.(ABSTRACT TRUNCATED AT 250 WORDS)