Withering syndrome (WS) is a debilitating and fatal disease of black abalone (Haliotis cracherodii) that is caused by a rickettsia-like organism (RLO). Foci of the RLO are found infecting the digestive tract (intestinal epithelia, and digestive tubule epithelia). The RLOs occur at extremely high levels in early infections, with less intense infections occurring in seriously afflicted abalone. The major sign of the syndrome, the withered and weakened foot, is an end-stage symptom of the disease. Populations of black abalone have been decimated by WS.  Red abalone (H. Rufescens) appear less affected by the disease. Laboratory observations suggest that they are more resistant to its effects. We undertook controlled laboratory studies to examine the efficacy of several antibiotic in treating afflicted abalone. Treatments consisted of injecting naturally infected abalone with low, moderate or high levels of specific anti-rickettsial antibiotics. Control groups of naturally infected abalone were injected with diluents. In daily doses over a two week course, we tested the following drugs for efficacy against the disease: chloramphenicol, tetracycline, sarafloxacin, and clarithromycin. Intramuscular injections were given to insure delivery. Tetracycline at 25 mg/kg and 50 mg/kg (body weight) was moderately to completely successful in ridding black and red abalone of RLOs. Surprisingly, chloramphenicol, sarafloxacin, and clarithromycin were not effective when given intramuscularly. Intermediate-Term, Long-Term and Oral dosing Trials indicated varying levels of efficacy of oxytetracycline dependent upon dose regimen, and timing of necropsy. Tetracycline and oxytetracycline may provide a potential treatment against rickettsial diseases of abalone.