Drugs produced through the use of recombinant DNA techniques have become an integral part of medical practice. Before recombinant FSH (rFSH) was introduced in 1996, FSH purified from the urine of postmenopausal women had been commercially available since the 1960s. We analysed the diffusion and the substitution patterns of the different FSH preparations in The Netherlands. The fact that rFSH preparations have batch-to-batch consistency, are free from urinary protein contaminants and have the potential to be produced in limitless quantities, is advantageous. The question whether newer, more pure FSH products are beneficial from the clinical perspective, has not been settled beyond reasonable doubt. The price of rFSH is three times as high as the price of the former FSH preparations. Due to the introduction of rFSH, total FSH expenditures have grown from 5.0 million Euros in 1995, to 26.8 million Euros in 2000, while the volume increased by <100%. Both the pharmaceutical companies and purchasers (government, insurers) have influenced the patterns of substitution of existing FSH products by biotech equivalents. In general, the risk of increasing pharmaceutical costs without clear clinical benefits has to be set against the risk of strangling innovations. Therefore, a continuous process of technology assessment is necessary.