We have evaluated the effects of induction therapy with foscarnet 100 mg/kg b.i.d. via i.v. infusion in 60 AIDS patients with cytomegalovirus (CMV) retinitis and compared the findings with those in 37 such patients receiving a foscarnet induction regimen of 60 mg/kg t.i.d. via i.v. infusion. Induction therapy was given for at least 3 weeks, with the treatment period being extended in cases of slow resolution of retinitis. There was no significant difference between response rates in the two groups, with ophthalmologic response being observed in 52 (96%) of 54 evaluable b.i.d. patients and 33 (97%) of 34 evaluable t.i.d. patients over mean durations of therapy of 26 and 27 days, respectively; complete and partial responses were observed in 91 and 6%, respectively, of b.i.d. patients and 85 and 12%, respectively, of t.i.d. patients. Foscarnet was discontinued because of adverse events in 3 (3%) of 97 patients, with treatment being stopped in 2 patients because of renal insufficiency and in 1 patient because of an acute neurologic disorder. Serum creatinine concentrations increased significantly in both the b.i.d. group (from 82 to 98 mumol/L, p less than 0.01) and the t.i.d. group (from 73 to 122 mumol/L, p less than 0.001), with the difference between increases not being statistically significant. Serum creatinine concentrations greater than 200 mumol/L were observed in two b.i.d. patients and four t.i.d. patients; in four cases, concomitant medications or conditions contributed to renal impairment. Hypocalcemia of less than 1.75 mmol/L occurred in 18% of b.i.d. patients and 28% of t.i.d. patients during treatment (p = 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)