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Low-volume azoospermia with an acidic ejaculate and absent fructose is highly suggestive of obstruction of the seminal vesicles/ejaculatory ducts. Transrectal ultrasound is the preferred next investigation because it non-invasively visualizes the seminal vesicles and ejaculatory ducts, confirming dilatation, cysts or calcifications indicative of obstruction and guiding further therapy [Hellerstein 1992, PMID 1580037; Patterson 1990, PMID 2231947].