The Y chromosome from spontaneously hypertensive rats (SHR) has a locus that raises blood pressure 20-25 mmHg. Associated with the SHR Y chromosome effect is a 4-week earlier pubertal rise of testosterone and dependence upon the androgen receptor for the full blood pressure effect. Several indices of enhanced sympathetic nervous system (SNS) activity are also associated with the SHR Y chromosome. Blockade of SNS outflow reduced the blood pressure effect. Salt sensitivity was increased by the Y chromosome as was salt appetite which was SNS dependent. A strong correlation (r = 0.57, P<0.001) was demonstrable between plasma testosterone and angiotensin II. Coronary collagen increased with blood pressure and the presence of the SHR Y chromosome. A promising candidate gene for the Y effect is the Sry locus (testis determining factor), a transcription factor which may also have other functions.