Abstract: To prepare E4A reagents used in BECKMAN Automatic Analyzer fr K⁺, Na⁺, Cl^-, and O₂ CP, some experiments were performed for preparing diluent buffer, acid dilurnt and lkaline uffer. Different preservatives were used in the study and the effective time of preservation as observed.The comparison of original BECKMAN E4A reagents commonly used with those prepared y ourselves showed no obvious difference, as indicated by statistical results, （1） K⁺, t=.750, P＞0.4; （2）Na⁺, t=1.026, P＞0.3;（3）Cl^-, t=0.898, P＞0.3;（4）CO₂CP, t=1.347, P＞0.1. The esults of practical clinical use in more than 10,000 cases also indicated that the local-made eagents can be used satisfactorily.