Our objective was to determine the effects of preshipping (PRE) vs. arrival (ARR) medication with tilmicosin phosphate (MIC; Exp. 1 and 2) and feeding chlortetracycline (CTC; 22 mg/kg of BW from d 5 to 9; Exp. 2) on health and performance of beef calves received in the feedlot. Ninety-six steers (Exp. 1; pay weight 236 kg) and 240 (Exp. 2; average pay weight 188 kg) steer and bull calves were used. For Exp. 1, treatments included no MIC (CON), PRE, and ARR. For Exp. 2, treatments were arranged in a 3x2 factorial. Treatments included CON, PRE, and ARR, either with CTC or without CTC. For Exp. 2, serum concentrations of immunoglobulin (Ig)G and alpha-1-acid glycoprotein (AGP) were determined on samples collected on d 0, 5, 10, and 28 and d 0, 5, and 10, respectively. No MIC x CTC interactions were observed. No differences were noted among MIC or CTC treatments in any of the experiments for ADG, daily DMI, or gain:feed ratio for the overall receiving periods. For Exp. 1, percentage of steers treated for bovine respiratory disease (BRD) was decreased (P<.05) for MIC-treated animals vs CON (71.9, 45.2, and 46.9 for CON, PRE, and ARR, respectively), and the week that calves were treated for BRD differed (P<.10) among treatments. For Exp. 2, the number of calves treated for BRD was decreased (P<.01) for MIC-treated steers vs CON and decreased (P<.05) for ARR vs. PRE (40.0, 18.7, and 7.5% for CON, PRE, and ARR, respectively). Averaged across days, serum IgG was decreased (P<.05) for MIC-treated steers vs. CON, with no differences noted among treatments for AGP. Results suggest that preshipping medication programs are no more effective than arrival medication programs using tilmicosin phosphate.