Delta-aminolevulinic acid (DALA), porphobilinogen (PBG) and porphyrins in urine and feces were determined in 40 healthy controls (20 males and 20 females) and in 60 patients with acute leukosis (27 males and 33 females), with chronic myeloleukosis - 23 (10 males and 13 females), and 25 patients with chronic lympholeukosis (II males and 14 females). Another 15 patients (7 males and 8 females) were studied at the initial stage, recurrence, recidivation of acute leukosis (AL). DALA excreted with the urine, manifested no significant discrepancy as compared with the controls of the three groups examined patients and in all the three stage of AL, whereas PBG was moderately reduced in the AL patients - initial stage and recurrence and was within the normal limits in the patients with chronic myeloleukosis (CML) and chronic lympholeukosis (CLL). The urine excreted coproporhyrin was increased, to various degrees, in the patients with CML and CLL and at the initial stage, recurrence and recidivation of AL, whereas uroporhyrin was within the norm. Coproporphyrin, excreted in the feces, was increased in all three groups of patients with leukosis and in the three stages of AL, whereas the other fractions showed no significant difference as compared with the controls. It could be concluded, from the results obtained, that porphyrins metabolism is disturbed in the patients with leukosis.