Toxicity studies with ammonium sulfate were scanty. Based on standard procedures, we estimated the 96 h acute toxicity of this agrochemical on the edible cockle, Anadara antiquata Linnaeus (Bivalvia: Arcidae), in a static in vitro bioassay at mean pH 8, temperature 28±1° C, salinity 33% and DO 6 mg/L. The LC50 was estimated at 270 mg/L±0.3 and mortality was 33.08% (4.56 probits), both at 95% significance level. Although the exposure was not acutely toxic, some uncontrolled massive deformities evidenced in the victims over 336 h. These postexposure injuries promoted mortality to 61.6% (5.3 probits) in which all samples exposed to 200 mg/L and above died. Stress manifestations involved excessive shell gaping, foot protrusion, mucus secretion coupled by necrosis, hyperplasia, cilial shortening, lamellar shrinkage, abscess formation and eventual epithelial ruptures and proliferations in the gills and gut. Prior to death, the victims lost mobility and sensitivity and their shell gaps were abnormally expanded. However, around 38.4% of all specimens survived this acute exposure, and the overall injury ranged between acute and chronic levels hence was subchronic. These results are indicating that A. antiquata has great potential of biomonitoring the toxicity of ammonium sulfate. A necessity for handling this agrochemical conscientiously is also justified.