Three balance feeding trials were performed with 3 groups male castrated pigs during the starter, grower and finisher periods. The animals were housed in specially designs individual cages that allowed for separate collection of urine and faeces. Each trial comprised 5 days preliminary and 5 days experimental period. Pigs were fed compound feeds according to their genotype and age. The first groups received compound feed without exogenous phytase. The feed of the second group was supplemented with the Bulgarian enzyme preparations Optiphos at 0.01 %, аnd the feed of group III – with the same amount of the enzyme preparation Natuphos. The results showed that the inclusion of exogenous phytase in compound feeds for pigs permitted to decrease the amounts of used dicalcium phosphtate by 3 to 7 times. This reduced the amount of total dietary phosphorus by 27-30 % and the cost of feeds. The utilization of phytase improved the absorption of phosphorus by 28-34 % and decreased its total output by 38-45 %, without any effect upon nitrogen retention. The performed trials did not shown any significant difference between the effects of both exogenous phytases used: Optiphos and Natuphos.