A human cell line LMS6-93 has been established from a leiomyosarcoma (LMS). Characteristics for ultrastructure, growth characteristics, cell cycle distribution, karyotype, protein expression detected by immunohistochemistry (IHC), p53 mutational status and liposomal transfection behaviour were studied and determined. The primary tumor was clearly positive for á-smooth muscle type actin and desmin in moderately differentiated areas and indicated a loss of myogenic differentiation in other regions and therefore was classified as a poorly differentiated LMS. The cell line LMS6-93 contains mainly polymorphic spindle shaped or polygonal tumor cells which possess the characteristics of primitive mesenchymal cells, based on their morphology and positive reaction with an antibody to vimentin. IHC staining for S100, synaptophysin A, NSE, neurofilament proteins and cytokeratins were negative. Cytogenetic analysis revealed in the cell line diploid karyotypes comparatively close to several structural and numerical aberrations for chromosomes 2, 5, 6, 9, 10, 12, 14, 17, 18, 20, 22, and Y. IHC positivity was found for the tumor suppressor protein Rb and the oncogene product MDM2. In a p53 mutational analysis a 1 bp insertional mutation in exon 6 (G insertion in codon 215) was detected and confirmed in the original primary tumor. The other p53 allele appears to be wild-type as indicated in Western hybridization. Using different cationic lipid formulations complexed with a reporter expression vector (GFP) successful transfection into LMS6-93 cells was observed. The highest transfection rates (20-30% GFP expression in the viable cell population) were obtained with lipofectin. These results suggest that LMS6-93 functions as a good in vitro model for transfection studies on an LMS cell line carrying a heterozygous p53-frameshift mutation.