Viable and non-viable cells in coronary and internal thoracic arteries, collected at autopsy 7-24 h post-mortem from individuals 15-81 years of age, were detected using the fïxable fluoroprobes 5-chloromethylfluorescein diacetate (green) and ethidium homodimer-1 (orange/red). Viability status of individual endothelial and smooth muscle cells was confirmed by simultaneous autoradiographic detection of incorporated [<sup>3</sup>H]glucosamine. Twenty-five percent of coronary and 42% of internal thoracic arteries contained viable cells up to 24 h following death. For the majority of viable vessels the mean percentage of viable cells ranged between 60 and 80% with no significant difference between coronary and internal thoracic arteries and no relationship with either age of the donor or with time to autopsy. Non-viable cells were usually distributed fairly evenly amongst viable cells but this pattern could not be assumed. In a number of vessels non-viable cells were variably clustered in different regions of vessel wall. These findings confirm that vessels sampled at autopsy can be used for metabolic studies with the caveat that assessment of cell viability is a necessary prerequisite for interpretation of results.