119 collections of peripheral blood stem cells were performed in 60 patients suffering from various haematological malignancies. One patient was transplanted twice. Peripheral blood stem cell mobilisation was performed using various regimens. A correlation (r = 0.732) was found between the number of peripheral CD34+ cells and the number of CD34+ cells that were collected by apheresis. Furthermore, the number of collected peripheral blood stem cells correlated with the number of colony-forming units (CFU-GM) identified after cell culture (r = 0.607). After transplantation, the duration of neutropenia (> 0.5 x 10(9)/l) was 11.7 days (SD = 3.3) and of thrombocytopenia (> 20 x 10(9)/l) 12.7 days (SD = 6.8). For the whole group, no correlation was observed between the number of CD34+ cells infused and the length of the aplasia. However, when the patients were separated into two groups, according to the amount of CD34+ cells transplanted (< 10 x 10(6)/kg, n = 48 and > 10 x 10(6)/kg, n = 13), a statistically significant but moderate decrease in the duration of neutropenia and thrombocytopenia was observed in patients who received the highest doses of CD34+ cells. Our results confirm the utility of measuring the number of the CD34+ cells in peripheral blood as well as in the product collected by apheresis, but they challenge the place of cultures of progenitor haematopoietic cells. Moreover, the infusion of large amounts of CD34+ cells shortens the duration of the aplasia.