The kinetic behaviour of bovine erythrocyte Cu-Zn SOD was investigated in Sprague Dawley male rats after subcutaneous and oral administrations of doses ranging from 0 center dot 5 to 20 mg kg-1. Studies have been carried out with SOD and SOD encapsulated into liposomes containing or not containing ceramides. The maximum concentration (Cmax) in blood cell pellets ranged from 8 center dot 65 to 11 center dot 03 U/mg haemoglobin (Hb) after subcutaneous injection, and from 4 center dot 48 to 8 center dot 23 U/mg Hb after oral administration. The maximum concentrations were reached in 5 h (t max) for the two routes. Comparison between the areas under the curves (AUCs) obtained after subcutaneous and oral administration allowed the calculation of relative bioavailability (F'). The maximum bioavailability after oral administration was 14% for free SOD, 22% for SOD encapsulated into liposomes, and 57% when ceramides were added to liposomes. Poor SOD bioavailability was enhanced by liposome encapsulation, and ceramide addition seemed to be beneficial for oral encapsulated SOD administration.