a simple, easy and quick eia for antibody to treponema pallidum (tp) was developed. it is tentatively called dd-eia (dot diffusion enzyme immunoassay). the center of glass fiber (quartz preferred) filter paper is marked as a tiny dot with a pencil. 25 to 50 ul (depending on antigen concentration) of antigen solution is placed on the mark and incubated at room temperature for 10 to 30 minutes. it is dried in an oven for 15 minutes. 50 to 100 ul of undiluted normal goat serum is placed on the mark for about 10 minutes to overcoat the antigen and its surrounding areas, and dried again as above. the antigen coated filter paper is stored with desiccants at 4 c. to assay, the following are added in sequence: (1) 25 to 50 ul of test serum sample; (2) two drops of wash solution; (3) one drop of alkaline-phosphatase labeled goat antibody to human igc (conjugate); (4) two drops of wash solution; (5) one drop of 5-bromo-4-chloro-3-indolyl phosphate; and (6) two drops of wash solution. the results, a blue spot for positive reaction, are read at the end of step 5 and 6, as step 6 washed away some color developed the test takes less than 7 minutes and the used filter papers can be dried and kept as a permanent record. test on a panel of serum samples from normal subjects and syphilis patients revealed good results