Compliance with the guidelines of the National Advisory Group on Standards and Practice Guidelines for Parenteral Nutrition (NAG) was studied. A questionnaire based on the NAG guidelines was developed to identify common practices used in the preparation of parenteral nutrition formulations in a variety of health care settings. The questionnaire was mailed in January 2000 to a national sample of 1445 pharmacists. There were a total of 633 usable responses, for a net response rate of 45.2% (based on 1400 deliverable surveys). Almost 80% of the respondents were employed in an urban setting, and 64.3% worked in hospitals. Relatively high compliance was reported for guidelines related to filtration (86.9% and 85.9%), verification of product stability and compatibility by a pharmacist or computer program (86.4%), evaluation of the aseptic technique of persons preparing sterile products (81.4%), and having a pharmacist assess formulations to determine whether the contents are within acceptable standard ranges (78.8%). Low compliance was reported for guidelines related to the inclusion of dosing weight on the label (15.4%), the use of amount per day as the unit of measure for labeling ingredients (26.1%), direct pharmacist-to-pharmacist communication about prescriptions when patients are transferred among health settings (33.4%), and daily in-process or end-product quality assurance testing of formulations. The NAG guidelines on parenteral nutrition formulations with which pharmacists' practice was most discrepant were the use of amount per day as the unit of measure for labeling ingredients, inclusion of the patient's dosing weight on the label, direct pharmacist-to-pharmacist communication when patients are transferred, and daily quality assurance testing.