OBJECTIVE To assess the clinical outcome and pharmacokinetics of therapy with cefazolin for patients with cellulitis in a hospital-in-the-home (HIH) program. METHODS Observational study with outcome data compared with previously published reports of therapy for cellulitis. METHODS A university teaching hospital and HIH unit, July 1996-December 1997. METHODS Patients with cellulitis were eligible for inclusion provided their medical condition was stable, they did not require surgical intervention, and their social circumstances allowed home-based therapy. METHODS Cefazolin 2 g intravenously twice daily, with regular nursing and medical assessment. METHODS Clinical efficacy; peak and trough serum concentrations of cefazolin. RESULTS Fifty-seven patients (37 were men) with a mean age of 48 years (range, 18-90 years) had 61 episodes of moderate to severe cellulitis (41, lower limb; 17, upper limb; and three, face). They received a median of 11 doses of cefazolin (range, 3-27 doses). Clinical outcomes were: cure in 54, improvement in one, treatment failure in three, and in the remaining three episodes the outcome was indeterminate. Cefazolin concentrations were measured in 27 patients. All peak concentrations were more than 40 micrograms/mL, while trough concentrations were all above the MIC90 of the expected pathogens: median, 3.2 micrograms/mL (range: 0.4-18.5 micrograms/mL). Cefazolin was well tolerated. CONCLUSIONS Twice-daily cefazolin 2 g intravenously is a convenient and effective option for home-based treatment of patients with cellulitis. Its clinical efficacy is comparable with other treatment regimens.