Diffusion is the process whereby a technology enters and becomes part of the health-care system. In the present study, diffusion of microbiological root canal sampling (MRS) among general dental practitioners within the city of Gothenburg was observed for 25 years, from the establishment of the Laboratory of Oral Microbiology in 1966. Laboratory records at 5-year intervals were analysed and adopters were categorized as 'occasional' (1-2 samples/year), 'selective' (3-10) or 'regular' (> 10) samples. The diagnostic accuracy was assessed by analysing the results of culturing 574 samples referred in 1986. The acceptance rate varied between 2.9 and 5.1% except in 1986 when 10.1% of the practitioners in the area referred root-canal samples. While a minority of the adopters used MRS as a standard procedure, the strategy appeared to be directed towards selection of special cases. The results of culturing revealed a predominance of facultatives. Although evidence of contamination was found, the practitioners frequently appeared to produce valid microbiological samples.