This experiment was carried out to study on changing phases of the concentrations of serum testosterone and metabolites in the various grwoing stages of male pigs. The eight males were used to obtain serial blood samples at a, pp.oximately 20kg body weight intervals from birth to 130kg body weight. The blood samples were taken from the jugular veins and serum was stored at -20$^{circ}C$ until assay. Testosterone concentrations in the serum were analyzed by radioimmunoassay. The result obtained are as follows: 1. Serum testosterone concentrations were elevated at birth and were reached a maximum level between 50 and 70kg body weight, which was when sexual maturity was reached. 2. Calcium values did not vary a, pp.eciably with body weight, and ranged from 9.6${pm}$0.6 to 11.9${pm}$0.8mg/100$mell$. Potassium and sodium concentrations ranged from 38.5${pm}$2.9 and 233.9${pm}$2.1mg/100$mell$ to 64.2${pm}$6.5 and 269.1${pm}$9.5mg/100$mell$, respectively. Magnesium values dro, pp.d at birth and then rose to peak at 15kg of body weight. Iron concentrations was 0.12${pm}$0.02mg/100$mell$ at birth, rose to 0.20${pm}$0.04mg/100$mell$ at 15kg of body weight and then gradually increased to 0.29${pm}$0.04mg/100$mell$ at 30kg of body weight. Serum zinc concentrations rose from a low of 56${pm}$3.3mg/100$mell$ at birth to a high of 83.3${pm}$3.4mcg/100$mell$ at 15kg of body weight. Co, pp.r values rose from a low of 25${pm}$2.5mcg/100$mell$ at birth to a high of 183${pm}$4.3mcg/100$mell$ at 15kg of body weight. 3. Serum cholesterol concenrtration did not vary a, pp.eciably with body weight, and ranged from 90.5${pm}$6.0mg/100$mell$ to 95.0${pm}$6.3mg/100$mell$. Glucose concentrations ranged from 80.5${pm}$1.2mg/100$mell$ to 108.7${pm}$8.4mg/100$mell$. Serum total protein rose from alow of 2.7${pm}$0.8mg/100$mell$ at birth to a rapidly high of 4.3${pm}$0.1mg/100$mell$ at 15kg of body weight and then gradually increased to 7.3${pm}$0.4mg/100$mell$ at 130kg of body weight. Serum albumin values ranged from 0.5${pm}$0.1$mell$ to 3.0${pm}$0.3mg/100$mell$. 4. The total concentrations of essential/nonessential amino acid were 944.7mg/100$mell$ and 934.4mg/100$mell$ at birth, respectively. The values of essential/nonessential amino acid gradually rose from a low level at birth to a high level at 130kg of body weight. The total concentrations of essential/non-essential amino acid ratios remained from birth to 130kg of body weight.