A 3-week-growth trial was conducted to investigate the effects of chromium picolinate, L-carnitine, and thyroxine on the growth performance, nutrient digestibility, and N balance in starter pigs. Eighty starter pigs (Landrace x Yorkshire x Duroc, 21±2 days of age, 5.4 kg of average initial body weight) were employed in a completely randomized block design with four treatments: 1. Control: without additives, 2. CrP: control diet + 0.05% of chromium picolinate, 3. Carnitine: control diet + 0.5% of Camifeed (10% of carnitine), 4. Thyroxine: control diet + L-thyroxine injection (0.1 mg/day/head), 5 replications and 4 heads per pen. Although there were no significant differences (P>0.05) in average daily gain (ADG) and average daily feed intake (ADFI), all of the pigs supplemented with CrP, L-carnitine and thyroxine grew better than pigs in the control group. Pigs fed L-carnitine showed the best ADG (15% of improvement compared with control group) through the entire experimental period and feed/gain ratio was improved (P<0.05). Digestibilities of energy, dry matter, crude protein and crude ash were improved (P<0.05) by the inclusion of L-carnitine, chromium picolinate or injection of thyroxine. Pigs fed chromium picolinate showed the best nutrient digestibilities. In a N balance trial, excreted N was lower (P<0.05) in pigs of all treated groups than in the control group. The N in feed also was more efficiently retained in pigs of treated groups. The DNA content of the liver was higher (P<0.05) in all treated groups. Only the pigs fed L-carnitine showed a higher (P<0.05) RNA content. The protein content of the liver tended to be higher (P>0.05) in pigs fed chromium picolinate or injected L-thyroxine. Total liver DNA, RNA and protein contents were higher (P<0.05) in pigs fed L-camitine. It may be concluded that chromium picolinate, L-carnitine and thyroxine may be useful for improving growth rate, nutrient digestibilities, and N balance in pigs weaned at 21 days of age, although the feasibility of an economic return seems quite weak.