Rapid diagnostic tests (RDTs) for malaria may help rationalize antimalarial drug use. However, the economic effects of these tests may vary. Data on costs were collected from 259 patients in 6 health facilities by using exit and in-charge interviews and record reviews during a trial of RDT rollout in Dar es Salaam, Tanzania. The RDTs decreased patient expenditure on drugs (savings = U.S. $0.36; P = 0.002) and provider drug costs (savings = U.S. $0.43; P = 0.034) compared with control facilities. However, RDT introduction did not significantly reduce patients' overall expenditures (U.S. $1.02, 95% confidence interval [CI] = $0.76-$1.36 versus U.S. $1.33 95% CI = $0.99-$1.77) and may increase total provider costs (U.S. $3.63, 95% CI = $3.40-$3.89 versus U.S. $2.32, 95% CI = $1.99-$2.69) compared with control facilities. Clinician's compliance with test results was higher with RDTs than with routine microscopy (95% versus 82%; P = 0.002). The RDTs reduced drug costs in this setting but did not offset the cost of the tests, although they also resulted in non-monetary benefits, including improved management of patients and increased compliance with test results.