The aim of this work was to assess the impact of circulating guidelines for correct prescription practices of colony stimulating factors (CSF). Two hospital groups were compared, a 'guidelines' group (seven teaching hospitals) that circulated the guidelines and a control group (eight teaching hospitals) that did not. In addition, two periods were compared before and after distribution of the guidelines: from 17 February to 2 March 1996 and from 17 February to 2 March 1997. The assessment involved compliance with the guidelines for the following parameters: indications, dose regimen, time to start of CSF therapy and duration of CSF therapy between the control and guideline groups and also between the two periods. The population included 404 patients analyzed (209 in 1996 and 195 in 1997) for the indication of post-chemotherapy neutropenia. Total compliance in the first period (all four items) was 44.2% in the control group and 50.8% in the guideline group (nonsignificant), and during the second period was 31.9 and 59.6% in the two groups (p<0.001). During the first period, the differences in compliance with the guidelines for indication, dose regimen, time to start of treatment and duration between the groups were not significant. In the second period, this difference became significant and in favor of the guideline group for dose regimen (p = 0.009) and treatment duration (p = 0.02). The results of this study show the need to continuously define prescription reference systems according to available data, and to circulate them widely to improve the quality of health care and to control expenses.