Several studies have investigated the influence of clinical and biological variables on mobilisation of peripheral blood progenitor cells (PBPCs). The aim of this study was to evaluate the role of steady-state bone marrow (BM) CD34+ cells as a predictive parameter of PBPC yield. We studied 90 patients with multiple myeloma (MM) (41 patients), non-Hodgkin's lymphoma (NHL) (25 patients) or acute myeloid leukaemia (AML) (24 patients), mobilised with chemotherapy and growth factor. The median time from first treatment to mobilisation was 5 months. Only one patient was previously exposed to alkylating agents. The median BM CD34+ count at mobilisation was 833 microl(-1) (range: 1.4-15.540) corresponding to 1.51% of mononuclear cells (range: 0.02-8.6). Sixty-six patients (73%) reached the optimal target of 4 x 10(6) kg(-1) CD34+ cells with 1 (18 patients), 2 (42 patients) or 3 leukaphereses (6 patients). Eleven patients (12%) mobilised less than 4 x 10(6) kg(-1) CD34+ cells and 13 (15%) failed mobilisation. Among the laboratory and clinical parameters evaluated at the time of mobilisation, only BM CD34+ count was a predictive factor for adequate collection (P = 0.04), particularly in MM patients (P = 0.003). In this setting, a BM concentration of CD34+ cells lower than 66 microL(-1) was associated with a higher probability of inadequate collection.