A microbore high-performance liquid chromatographic method with electrochemical detection was developed for the measurement of small quantities of dopamine and its metabolites, 3,4-dihydroxyphenylacetic acid and homovanillic acid, in microdialysis samples from rat striatum. The limit of detection of dopamine was in the low nmol/l range (10 fmol/40 microliters dialysate). Standard mixtures of dopamine and its metabolites were stored in tubes made of polypropylene, soda-lime glass or borosilicate glass. Dopamine and homovanillic acid were stable in all three types of container for 24 h providing they were kept at an acidic pH. However, 3,4-dihydroxyphenylacetic acid was only stable in tubes made of polypropylene or borosilicate glass. Basal levels of dopamine in the dialysate obtained from rats which had been chronically implanted with a microdialysis probe in the anterior striatum were stable for one to three days following probe implantation. However, the levels of 3,4-dihydroxyphenylacetic acid and homovanillic acid in the dialysate decreased rapidly with time after the first day. This indicates that the synthesizing capacity of the neurons is compromised by the microdialysis probe after day one, and that microdialysis experiments in freely moving animals should be confined to the day immediately following probe implantation.