The effect of cyadox on growth and apparent digestibility of nutrients in weanling pigs was investigated. Cyadox (2-formylquinoxaline-N1,N4-dioxide cyanocetylhydrazone) is a derivative of quinoxaline-1, 4-dioxide, a growth promoting antimicrobial agent that is used in pig production. Seventy-five crossbred weanling barrows were randomly assigned to three treatments with five replicates per treatment. The three dietary treatments consisted of an unmedicated diet (control), a diet containing 100 mg/kg of cyadox and a diet containing 100 mg /kg of olaquindox. The body weight and feed consumption of the pigs were measured weekly for the 4-week experimental period. During week 4 a digestibility study was conducted, and faecal grab samples were collected for six days from each pen. The pigs fed cyadox had significantly higher average daily gains and improved feed conversion efficiencies compared to the control. Cyadox did not affect average daily feed intake. The apparent digestibility of dry matter, crude protein, ether extract, nitrogen free extract, calcium, phosphorus and gross energy was significantly increased in the cyadox-fed pigs above the control. Inclusion of cyadox significantly improved the apparent digestibility of iron, copper, zinc and manganese, and that of several essential and nonessential amino acids. It is suggested that the growth promoting effect of cyadox may be attributed to the improvement in the apparent digestibility of dietary nutrients.