These two cases illustrate many classical features of latrodectism. A subclinical bite followed by extensive systemic signs and symptoms in a recognizable pattern is strongly suggestive of the diagnosis. Pain and muscle spasms are refractory to standard therapy but are relieved by intravenous calcium. Finally, there should be complete resolution of the symptoms after only one vial of antivenin is administered. The common features of these cases form a recognizable constellation of signs and symptoms known as latrodectism. The specifics of these cases highlight the uncertainty of therapy. The older patient, because of the severity of his symptoms, warranted the use of antivenin perhaps earlier than it was given. The argument could be made, however, that because the patient was experiencing minimal morbidity and mortality, the calcium would have controlled his symptoms until the venom was cleared from his system. There would then have been no risk of anaphylaxis or serum sickness. One can only guess whether continued calcium use would have precipitated a hypercalcemic state and also would have been a health risk. The decision to provide antivenin therapy was made and the patient did well. The younger patient was not as severely affected as the older patient, so it could be argued that he was less in need of the antivenin. Still, his symptoms had not abated despite a reasonable length of time and might even have been considered to be worsening. No bite was found, but having discovered him playing with the spider certainly qualifies as circumstantial evidence. Also, the child was 11 months old and had greater risk of mortality.(ABSTRACT TRUNCATED AT 250 WORDS)