Expressions of IgG genes were analysed in the sera of piglets of Line 990 and crosses of Line 990 with Polish Large White and Polish Landrace. The analysis involved the course of synthesis of immunoglobulins – carriers of 14 heavy-chain markers and one light-chain marker in 143 piglets from birth to the fifth month of age. The antigenic markers were determined in agar gel using specific alloantibodies against individual epitopes. From the presence (or absence) of an epitope (antigen) the presence (or absence) was concluded of the respective protein, and indirectly the expression of a given gene. Although in some piglets the expression of immunoglobulin genes was found as early as by day 14 of age, in most animals it first appeared at the age of 1-2 months, and in some even later, i.e. at the age of 4 months.