Sparfloxacin (SPX), a novel fluoroquinolone with a broad spectrum of antibacterial activity, has been shown, in vitro, to be more effective against common pulmonary pathogens, particularly Streptococcus pneumoniae, Mycoplasma pneumoniae and some intracellular organisms, than ciprofloxacin (CPX). The objective of this open, comparative, randomized study in two parallel groups was to assess the serum concentrations and penetration of SPX and CPX into alveolar macrophages (AMs), epithelial lining fluid (ELF), and peripheral polymorphonuclear leucocytes (PMNs). Patients received either a single oral dose of SPX, 400 mg (16 patients), or CPX, 500 mg (15 patients), at various times before a routine diagnostic bronchoscopy was performed. Antibiotic concentrations were determined by using a microbiological assay. The median serum elimination half-lives were 17.3 h for SPX and 5.3 h for CPX. Peak levels (median+/-68% confidence range) of CPX were attained in AMs (7.6+/-1.7 mg x L(-1)) at 5 h after admission, and in both ELF (2.13+/-0.91 mg x L(-1)) and PMNs (9.1+/-6.2 mg x L(-1)) at 2.5 h after administration. SPX achieved comparable peak levels in PMNs (median+/-68% range, 9.4+/-1.1 mg x L(-1) at 5 h), but peak concentrations attained in AMs and ELF (35.1+/-15.4 and 32.2+/-28.2 mg x L(-1), respectively, at 24 h) were several times higher than those of CPX. SPX demonstrated substantially greater accumulation in all three sites than did CPX (peak site to serum ratios of 11.0+/-4.3, 65.5+/-28.4 and 63.0+/-66 versus 4.94+/-0.64, 10.6+/-3.7 and 10.6+/-3.7 for PMNs, AMs and ELF, respectively). The results indicate, that sparfloxacin has a long elimination half-life and that it achieves higher concentrations in alveolar macrophages and epithelial lining fluid than ciprofloxacin. Site concentrations of sparfloxacin greatly exceeded the minimal inhibitory concentrations of common respiratory pathogens.