The latest review included a full audit carried out by an assessor from the American Association for Laboratory Accreditation (A2LA).
It involved assessing STRI's quality procedures and American Society of Testing & Materials (ASTM) compliance.
STRI head of soils and sport surface science Dr Stephen Baker said: "This is a great achievement and demonstrates our goal to continually deliver world-class testing, analytical and evaluation services to golf courses and other sports-turf facilities across the UK and Europe."
STRI remains one of only 10 USGA-approved physical soil-testing labs in the world.
Full details of all the testing services available from STRI can be found on the newly launched website at www.stri.co.uk/services.
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