Ethylenediamine dihydrochloride (EDA.2HCl) was incorporated into the diet and fed to Fischer 344 rats for 2 years at target doses of 0, 0.02, 0.10 or 0.35 g/kg/day (equivalent to 0.009, 0.045 and 0.158 g free EDA/kg/day). Two separate untreated control groups were used. Interim sacrifices were at 6, 12 and 18 months and the terminal sacrifice was at 24 months. Under the conditions of this study, EDA.2HCl was not carcinogenic in the Fischer 344 rat. Most toxic responses were observed at the 12-month sacrifice and thereafter. Reductions in mean body weight gain were observed in high dose group male rats throughout most of the study and in the high dose group of female rats after approximately 18 months. Conversely, there was a slight increase in the mean body weight gain for the medium level female rats from about day 21 until 21 months that was of equivocal biological significance. Increased mortality was observed in the high dose group of both sexes and the mid dose group of female rats. The cause of the decreased survival was unclear, but may have been related to the enhancement of background degenerative lesions such as chronic nephropathy. Throughout the study, male rats from the high dose group had decreased erythrocyte counts, haemoglobin concentration and haematocrit. The cause and biological significance of the haematological changes were unknown. Increased water consumption was observed in the high dose group of both sexes during the latter half of the study. Increased urine volume with concurrent decreased urine specific gravity was generally observed in the high dose group of both sexes in the last half of the study and suggested a possible alteration in kidney function. Altered urine volume and specific gravity persisted to termination in female rats only. Slight increases in absolute and relative kidney weights were also observed in the high dose group of female rats during the latter half of the study. Hepatocellular pleomorphism was observed in the high dose group of both sexes, especially the female rats, and may have contributed to increased mean liver weights observed primarily in female rats from the high dose group. Hepatocellular pleomorphism was first observed in female rats at 12 months but was not observed in male rats until the final sacrifice. Rhinitis and tracheitis were observed with greater frequency in the high dose group of male rats at 12, 18 and 24 months and in high dose group female rats at 18 months. At 24 months, rhinitis, but not tracheitis, persisted at a significantly greater frequency in high dose group female rats. The apparent no-observable-effect level (NOEL) of this study was at the lowest dose level, 0.02 g/kg/day (equivalent to 9 mg EDA/kg/day).