Over-estimation is an important drawback of the Human-capital approach (HCA) of calculating cost of lost productivity. Also, there is insufficient empirical research regarding the use of Friction-cost approach (FCA) in calculating cost of lost productivity. These factors have acted as barrier to incorporation of cost of lost productivity in cost analyses studies. OBJECTIVES: This study seeks to estimate and compare cost of lost productivity by Human-Capital Approach (HCA) and Friction-Cost Approach (FCA) in patients with asthma. METHODS: Cross-sectional analysis was conducted using MEPS household component and medical condition survey, 1996. Patients with asthma (ICD-9: 493), who were between the ages 16 to 65 years and had missed, at minimum, half a day of work were selected. Missed hours due to illness, hourly wages and benefits were calculated based on data provided in MEPS and Bureau of Labor statistics. Costs of lost productivity were estimated using the HCA and FCA methods. RESULTS: Of the 65 patients who were included in the study, 59% were full-time workers, 32% were part-time workers and 9% had changed their work status during the study period. Estimated total cost of lost productivity for 56 patients, by HCA, in 1996 was US$ 113 877 (1996 dollars). While, according to FCA, the estimated total cost of lost productivity ranged between US$ 64 014 and US$ 81 723 (1996 dollars). CONCLUSION: The study results demonstrate that FCA estimates of cost of lost productivity are relatively lower as compared to HCA estimate. Also, depending on assumptions considered in FCA, there could be large variations in cost of lost productivity, as observed in this study. Therefore, for meaningful incorporation of lost productivity in cost-analysis studies further refinement of these two methods is implied.