Since chlamydia in hard clams (Harshbarger, J.C., Chang, S.C., and Otto, S. V. 1977. Science, 196:666-668) failed to grow in a cell line known to be susceptible to human chlamydiae and rickettsiae (BSC-1 from the Cercopithecus monkey) and since there was a need of purified organisms for immunologic, biochemical and biophysical characterization, an infectivity study was attempted. Using a 1/16 inch bit, a hole was drilled through the shell and the digestive diverticulum was inoculated with 10% infected clam homogenate in seawater. Digestive tissue was removed on day 86, 114, 142, 170 and 202 post-inoculation, prepared for histopathologic study and examined for the Aathognomonic, pleomorphic, cytoplasmic inclusion bodies within the clam's digestive diverticular epithelium. Of 40 inoculated, seven clams (17.5%) showed inclusions, while only two clams (8.7%) of 23 seawater-inoculated controls had inclusions. One hundred untreated clams from the same batch examined just prior to the experiment had a 3% prevalence. The results of this study indicate that our method of inoculation was effective in the transmission of chlamydia in hard clams.