The concentration of elastic fibres in the male urethra during human fetal development. 
To describe the distribution of elastic fibres in the developing male urethra and to provide stereological data of the concentration of elastic fibres in the human urethra.  Urethras were obtained from 10 fresh normal human fetuses at 15-36 weeks of gestation.  A place-matched spongy urethra of a 27-year-old normal adult man was also analysed.  Samples were fixed in Bouin's solution, embedded in paraffin and histologically processed.  The elastic system fibres were evaluated by light microscopy using Weigert's resorcin-fuchsin technique after oxidation.  Morphometric values were assessed by the point-counting method.  The volumetric density (Vv) of elastic fibres was correlated with fetal age.  At 15 weeks the elastic fibres were sparse and homogeneously distributed.  The size and thickness of elastic fibres increased with age, mainly in the third trimester of gestation.  Elastic fibres formed a randomly orientated network in the trabeculae of the corpus spongiosum.  The mean (sem) Vv of elastic fibres in the spongy urethra was 5.2 (0.4)% in the fetus at 15 weeks and 14.8 (1.0)% at 36 weeks.  In the urethra of the place- matched young man the Vv was 19.0 (1.3)%.  The concentration of elastic fibres in the spongy urethra increased significantly with age.  The high concentration of elastic fibres in the spongy urethra may partly explain its high extensibility.  The progressive increase in elastic fibres during development implies functional adaptation of the fetal male urethra.