The increasing complexity of multiparameter data collection and analysis in flow cytometry and the development of relatively inexpensive arc-lamp-based flow cytometers, which increases the probability that laboratories or institutions may have more than one type of instrument, creates a need for shareable analysis programs and for the transport of flow cytometric data files within an installation or from one institution to another. To address this need, we propose a standard file format to be used for all flow cytometric data. The general principles of this proposal are: (1) The data file will contain a minimum of three segments, TEXT, DATA, and ANALYSIS; (2) The TEXT and ANALYSIS segments consist of KEYWORDS, which are the names of data fields, and their values; (3) All TEXT is encoded in ASCII; (4) KEYWORDS and their values may be of any length; (5) Certain KEYWORDS will be standard, i.e., having specified formats to be recognized by all programs. The structure of the DATA segment will be uniquely defined by the values of KEYWORDS in the TEXT area. It may be in any bit resolution, facilitating compatibility between machines with different word length and/or allowing bit compression of the data. The structured nature of the TEXT area should facilitate management of flow cytometric data using existing data base management systems. The proposed file format has been implemented on VAX, PDP-11, and HP9920 based flow cytometry data acquisition systems.