Blood from the defendant in the Westmeath rape trail provided a DNA matching with semen taken from the alleged victims panties, a jury at the Central Criminal Court has been told.
The jury already heard the accused voluntarily gave blood samples when arrested in 1996.
A forensic scientist, Dr Maureen Smyth, gave evidence of the procedures adopted in the laboratory in connection with samples provided and noted that DNA would also eliminate suspects.
A 56-year-old man pleads not guilt to nine charges of rape and indecent assault on the now 72-year-old woman on specific dates from 1983 to 1994.
Dr Smyth told Mr George Birmingham SC, prosecuting, her first tests on the blood and semen samples established the same blood group was involved in both.
About 7.5 per cent of the population belonged to the specific blood group, she told Mr Birmingham. This meant the accused could not be excluded as a suspect and she therefore proceeded to compare the samples for DNA profiling.
Dr Smyth said she only carried out two specific tests and her work provided a figure on one-in-850 chances of similarity. She said the laboratory had significant checks with the tests being witnessed by other scientists.
She agreed with Mr Birmingham that her findings were made available to an expert nominated by the defence.
The trial is being heard by Mr Justice Quirke and a jury.