In former studies short-term renal hypertension (2 weeks) in rats led to a remarkable increase of arterial smooth muscle cells (ASMC) proliferation in cultures and subcultures, examined by cell counting and 3H-thymidine indices /flasks in cultures or subcultures of hypertensive rats. The activated cell growth was observed up to the 6th subcultures. The proliferation of ASMC cultivated from short-term hypertensive rats is suppressed or eliminated respectively by antirheumatic drugs up to the 6th subcultures. Long-term renal hypertension (4-6 weeks) in rats showed the same increase in ASMC proliferation rate up to the 2nd subcultures but in the higher passages e.g. in the 6th subcultures the ASMC growth increase was not existing anymore. The limited reduplication capacity of postmitotic cells, we assume, is the cause of this difference.