The invention relates to a process for the preparation of a carrier particularly used in serological reactions, and to a carrier produced according to this process. The carrier consists of carbon comminuted to a grain size of 0.30-1.00 micron and suspended in a buffer having a pH-value of 8.2, preferably in a glycine buffer. The quantity of carbon suspended in the buffer should secure, when making the measurement on the spectrophotometer, a transparency of 10-15 percent. The obtained carbon suspension in a buffer having a pH-value of 8.2 is used in analytic reactions, particularly in serological ones.