The optimal time for starting G-CSF application after autologous peripheral stem cell transplantation (APSCT) still remains undetermined. All previous studies used 'fixed' days (0 or +1 vs +5 or +7 post-transplant) for this purpose. As many other drugs have individual, patient-dependent criteria (eg antibiotics, blood products, etc), and the discontinuation of G-CSF also has strict patient-dependent criteria (surprisingly absent when starting the drug) we suppose that attempts to find general criteria suitable for every patient may not be successful. In order to also take the patients' individual predispositions into account we designed a randomized clinical trial to compare 'immediate' administration of G-CSF (day +1: group A) vs 'delayed, patient-dependent' (first day when absolute neutrophil count (ANC) was below 0.5 x 10[9]/1: group B) therapy with G-CSF (both groups received 10 microg/kg/day i.v.). A total of 70 patients after APSCT suffering from non-Hodgkin's lymphoma (NHL) and Hodgkin's disease (HD) conditioned with BEAM, or from multiple myeloma (MM) after melphalan (L-PAM: 200 mg/m2) were enrolled in this study (35 in each group). Both groups were comparable with regard to age, sex, disease stage and previous therapy as well as the number of CD34+ cells transplanted. In group B, G-CSF administration began on day +4 post-transplant (+2 - +5). There were no detectable differences seen in the hematopoietic recovery (time to reach ANC more than 0.5 x 10(9)/l: 12 days vs 13 days; time to platelet recovery, more than 50 x 10(9)/l: 24 days in both groups), use of blood products or antibiotics, infections, or days of hospitalization. Delayed G-CSF application led to significant cost saving in terms of APSCT (approximately US$1341 for each patient). We suggest that 'patient-dependent' criteria for starting G-CSF are reasonable especially in patients conditioned with protocols only slowly inducing neutropenia: eg NHL and HD patients after BEAM, MM after L-PAM or patients after busulphan and cyclophosphamide (BUCY2).