Therapeutic biologics are often administered based on body size. A previous study has found that fixed dosing performs similarly to body size-based dosing in reducing intersubject variability in drug exposure across the mAbs studied. This study extended this evaluation to other therapeutic proteins and peptides. Eighteen therapeutic proteins and peptides with published population pharmacokinetic (PK) and/or pharmacodynamic (PD) models were selected for dosing approach evaluation. The relationships between body size and drug exposure (and PD end point when available) were evaluated, and simulation studies were conducted to compare the performance of the 2 dosing approaches. The results showed that fixed dosing performed better for 12 of 18 selected biologics in terms of reducing intersubject variability in exposure at both population and individual levels, whereas body size-based dosing performed better for the other 6 molecules. This result is consistent with the findings for mAbs. Therefore, fixed dosing is recommended for first-in-human studies of proteins and peptides along with mAbs. The final dosing approach for phase 3 studies should be determined based on a full assessment of body size effect on PK/PD when data are available and the therapeutic window of the drug.